Saturday

February 6, 2016
Number of results: 28,944

**maths**

Abc is a triangle where ad bisects angle a and d is the midpoint of bc prove that triangle is isosceles
*September 21, 2014 by parry*

**Math**

If the bisector of the vertical angle of the triangle bisects the base prove that the triangle is isosceles?
*August 20, 2011 by Syed*

**geometry**

AD is an altitude of an isosceles triangle ABC in which AB=AC. Show that AD bisects BC.
*September 21, 2011 by Anonymous*

**Geometry**

Can you help me with Always, Sometimes, Never questions?? I have answered all of these, but I am not sure if they are right. 1. The base angle of an isosceles triangle are acute----Always 2. When the altitude and the median are drawn from the same vertex of a triangle, the ...
*May 28, 2013 by Melissa*

**Geometry Honors**

Can someone help me with Always, Sometimes, Never questions?? I have answered all of these, but I am not sure if they are right. 1. The base angle of an isosceles triangle are acute----Always 2. When the altitude and the median are drawn from the same vertex of a triangle, the...
*May 28, 2013 by Melissa*

**Maths**

X and Y are points on the sides BC and AC of a triangle ABC respectively such that angle AXC = angle BYC and BX = XY. Prove that AX bisects the angle BAC. I believe the first step is to prove ABXY is a cyclic quadrilateral. Unfortunately, I dont know how!!!
*July 20, 2008 by Bobby*

**math**

The base of triangle ABC is one half the altitude.The altitude of triangle DEF is one half its base. If both triangles are equal in area, what is the ratio of the altitude of triangle ABC to the altitude of triangle DEF ? a. 1:4 b. 1:2 c. 1:1 d. 2:1 e. 4:1 please answer and ...
*April 19, 2014 by thomas*

**math**

The base of triangle ABC is one half the altitude. The altitude of triangle DEF is one half its base. If both triangles are equal in area, what is the ratio of the altitude of triangle ABC to the altitude of triangle DEF? a. 1:4 b. 1:2 c. 1:1 d. 2:1 e. 4:1 please answer and ...
*April 24, 2014 by thomas*

**Math(Geometry)**

In the diagram below(no diagram but details will be provided), right triangle ABC and line BD is an altitude to side line AC. * Prove that (AB)^2=(AC)(AD) -When you label the triangle B should be were the right angle is C should be at the top of the triangle and it should be ...
*November 24, 2010 by Phyllis *

**Geometry**

Given: segment BD bisects angle ABC; AB=BC. Prove: triangle ABD congruent to triangle CBD
*March 12, 2013 by Constance*

**Euclidean Geometry**

I am in the 10th Grade and my question is: The base of an isosceles triangle is 21cm. long. The altitude to the base is 9cm. long. What is the approx. measure of a base angle of the triangle? The tangent of that angle is 9/10.5 = 0.8571 Trigonometric tables will tell you that ...
*April 28, 2007 by Blake*

**Geometry- how to write proof**

ABC is a right triangle. Angle C is 90 degree. Altitude CD is drawn to hypotenuse AB. Prove AB/BC = BC/BD and AB/AC = AC/AD This is a theorem. How do I prove it? Thanks. Dont you have similar triangles? You can show this by looking at the angles involved...remember the ...
*February 23, 2007 by Jen*

**geometry**

TWO COLUMN TRIANGLE PROOF Given: line AB is parallel to line DE, and line AD bisects line BE Prove: triangle ABC is congruent to triangle DEC by using the ASA (angle-side-angle) postulate
*November 9, 2008 by tori*

**geometry**

if the isosceles triangle abc has one base angle of 2x-20 and the other base angle x+10 then what is the measure of angle b given the choices 36,40, 44, and 48
*December 31, 2011 by ashanti*

**corollary to isosceles triangle theorem**

how to prove 1)the measure of each angle of an equilateral triangle is 60. 2)the bisector of the vertex angle of an isosceles triangle is the perpendicular bisector of the base. Thanks. 1) The angles in any triangle have to add up to 180 degrees, right? 3 x 60 = 180 2) ?? 2. ...
*November 17, 2006 by Jen*

**SAT math**

Can someone please double check my true and false answers! 1. All cylinders are prisms: TRUE 2. The angle opposite a side length of 6 cm in a triangle is larger than an angle opposite a side length of 7 cm in the same triangle: FALSE 3. The perpendicular bisector of the base ...
*June 2, 2013 by mysterychicken*

**Geometry**

1. In an isosceles triangle that is not equilateral the angle between the congruent sides is called a ____ A> Leg B> Vertex C> Base D> Corollary <<<<<<<<THIS ONE 2. In triangle ABC, AB = CB, m<ABC = 4x-3, and m<CAB = x-3. What is m<...
*December 11, 2015 by Chase*

**maths**

in triangle abc angle b = 2angle c.d is a point ob bc such that ad bisects angle bac and ab = cd.prove that angle bac = 72
*August 15, 2012 by rajat garg*

**Isoceles Angle Bisector**

Triangle ABC is isosceles with AB=AC. D is a point on BC such that AD bisects ∠BAC. What is the measure of ∠ADB (in degrees)?
*April 19, 2013 by HELP ME...uRGENT!...PLEASE*

**Geometry**

Do the altitudes of an isosceles triangle go to the midpoints of the opposite sides? My triangle ABC is isosceles with points A (0,0), B (a,b), and C (2a,0). My diagram shows that the altitude from A will hit side BC at point N and the altitude from C will hit side AB at point...
*November 30, 2008 by Amy*

** Geometry **

In triangle ABC, AD bisects angle A, BD=4 and CD=5. The perimeter of triangle ABC is 29. Find the lengths of AB and AC.
*January 5, 2016 by Anonymous*

**Geometry **

Please answer at least one . PLEASE 1. Triangle XYZ has a right angle at Y. V,W are on XZ such that XV=XY. WZ=YZ, find ANGLE VYW . 2. STUVWXYZ is a regular octagon. Find SW/ TZ. 3. The interior angles of a convex polygon form an arithmetic progression with a common difference ...
*October 19, 2013 by Jayden*

**12th grade**

Find altitude of isosceles triangle if angle=53 degrees and base is 8 inches.
*December 2, 2010 by Ro*

**trig**

Find the altitude of an isosceles triangle whose base in 30 cm vertex angle is 75 degres
*February 11, 2011 by ...wew*

**Geometry **

Let ABC be any triangle. Equilateral triangles BCX, ACY, and BAZ are constructed such that none of these triangles overlaps triangle ABC. a) Draw a triangle ABC and then sketch the remainder of the figure. It will help if (triangle) ABC is not isosceles (or equilateral). b) ...
*March 19, 2015 by G*

**geometry**

the base of an isosceles triangle is 18 centimeters long. The altitude to the base is 12 centimeters long. What is the approximate measure of a base angle of the triangle?
*June 30, 2010 by SL*

**geometry proofs**

given ABC is a triangle. Ad is the altitude to BC. Ad biscects angle BAC. Prove: Ad is the median to BC
*December 14, 2010 by SKipper*

**geometry**

how do you find the height of an isosceles triangle only knowing the lengths of all three bases? EX: There's isosceles triangle ABC with vertex angle B. AB= 5x-28. BC= 2x+11. AC= x+5
*January 15, 2010 by erin*

**geometry**

the vertices of triangle ABC are A(1,7)B(9,3)C(3,1) a.prove that the triangle is a right triangle b.which angle is the right angle? c.which side is the hypotnuse? d.what are the coordinatesof the midpoint of the hypotnuse? e.what is the equation of the median from the vertex ...
*February 20, 2009 by melissa*

**trig**

Find altitude of isosceles triangle if angle=53 degrees (the equal angles) and the base is 8 inches.
*December 2, 2010 by Ro*

**geometry**

Each base of an isosceles triangle measures 42 degrees, 30'. The base is 14.6 meters long. a. Find the length of a leg of the triangle b. Find the altitude of the triangle c. What is the area of the triangle?
*October 27, 2012 by Sofia*

**Geometry**

The altitude to the hypotenuse of a right triangle ABC divides the hypotenuse into 12mm and 16mm segments. Find the lengths of each of the following. A. The altitude to the hypotenuse B. The shorter leg of angle ABC C. The longer leg of angle ABC
*September 30, 2013 by George*

**GEOMETRY**

GIVEN: TRIANGLE ABC,AD bisects <BAC,and AE=ED, PROVE:AE/AC=BD/BC
*September 17, 2012 by HELEN*

**Geometry - semicircle inside isosceles triangle**

Isosceles triangle ABC has sides of length AB=AC=25 and BC=40 . Find the area of a semicircle inscribed in triangle ABC with diameter along BC . Please help I do not know how to start....
*March 21, 2013 by Knights*

**Geometry**

The perimeter of triangle ABC is 29 meters. Line segment AD bisects angle A. Find AB and AC. CD=5cm, DB=4 cm.(triangle angle bisector theorem)
*December 28, 2011 by Lily*

**mathematics**

in triangle abc if acosA= bcosB then how to prove the triangle is isosceles or right angled
*September 20, 2012 by edward*

**Math**

In triangle ABC, D bisects side BC, G bisects side AB, and the points E and F trisect side AC. What is the area of the shaded polygon, if the area of ABC is 108? I tryed to find the area of triangles on the side and I figured that if you put a line from the top of the triangle...
*December 7, 2013 by Lily*

**Math**

In triangle ABC, D bisects side BC, G bisects side AB, and the points E and F trisect side AC. What is the area of the shaded polygon, if the area of ABC is 108? I tryed to find the area of triangles on the side and I figured that if you put a line from the top of the triangle...
*December 7, 2013 by Lily*

**Math please help urgent**

In triangle ABC, D bisects side BC, G bisects side AB, and the points E and F trisect side AC. What is the area of the shaded polygon, if the area of ABC is 108? I tryed to find the area of triangles on the side and I figured that if you put a line from the top of the triangle...
*December 7, 2013 by Lily*

**wgu qlc**

isosceles proof prove that angle dgf is isoceles given line eg bisects angle def edg is congruent to efg
*September 23, 2013 by shonda*

**Math-CHECK PLEASE**

Which of the statements is ALWAYS TRUE? A-A right triangle is a scalene triangle. B-An equilateral triangle is an isosceles triangle. C-An isosceles triangle is an obtuse triangle. D-A right triangle is an acute triangle. I got either A or D. I don't know. Also, if angle A is ...
*March 8, 2011 by Catherine*

**9th grade**

given that a(-1,8) ,b(2,4) and if the line y=4 is the axis of symmetry of triangle abc find c.show that triangle abc is an isosceles triangle,calculate the area of triangle abc,calculate the perpendicular distance from a to bc
*March 23, 2010 by anum*

**Trigonometry**

Each base angle of an isosceles triangle measures 42°. The base is 14.6 feet long. A) Find the length of a leg of the triangle. Round to the nearest tenth of a foot. B) Find the altitude of the triangle. Round to the nearest tenth of a foot.
*February 25, 2010 by Laly *

**Trigonometry**

Each base angle of an isosceles triangle measures 42°. The base is 14.6 feet long. A) Find the length of a leg of the triangle. Round to the nearest tenth of a foot. B) Find the altitude of the triangle. Round to the nearest tenth of a foot.
*February 26, 2010 by Stephanie*

**math**

an altitude of triangle is 5/3rd of the length of its corresponding base if their altitude be increased by 4cm and the base is decreased by 2cm, the area of the triangles remain the same. find the base and altitude of triangle ?????
*October 7, 2012 by TUHITUHI*

**Math**

Triangle ABC is an isosceles triangle with angle A= 40 degrees. Give three possible values for angle B
*May 7, 2014 by Mackenzie*

**geometry**

Triangle ABC is an isosceles triangle, where angle B is the vertex angle. If BC = 10x-4 , AC= 2x+18 , and AB= 6x+32, find the value of x.
*December 15, 2010 by tim*

**geometry**

I have right triangles I need to solve. Can you see if I am doing them correctly or screwed up..1) Rt < is in left corner C: Opposite is 60 deg< A, last angle is at top- 30 deg <. line segment of AB is 10. Hypo is f. I got 10 0r 12.5 for answer. 2) Triangle is ABC ...
*April 20, 2015 by robin*

**geometry**

Points D, E, and F are the midpoints of sides \overline{BC}, \overline{CA}, and \overline{AB} of \triangle ABC, respectively, and \overline{CZ} is an altitude of the triangle. If \angle BAC = 71^\circ, \angle ABC = 39^\circ, and \angle BCA = 70^\circ, then what is \angle EZD+\...
*July 23, 2014 by kat*

**geometry**

Points D, E, and F are the midpoints of sides \overline{BC}, \overline{CA}, and \overline{AB} of \triangle ABC, respectively, and \overline{CZ} is an altitude of the triangle. If \angle BAC = 71^\circ, \angle ABC = 39^\circ, and \angle BCA = 70^\circ, then what is \angle EZD+\...
*July 23, 2014 by kat*

**Geometry **

Points D, E, and F are the midpoints of sides \overline{BC}, \overline{CA}, and \overline{AB} of \triangle ABC, respectively, and \overline{CZ} is an altitude of the triangle. If \angle BAC = 71^\circ, \angle ABC = 39^\circ, and \angle BCA = 70^\circ, then what is \angle EZD+\...
*December 16, 2014 by Krash*

**math**

in an isosceles triangle ABC ,AB=AC.if AB and AC are produced to D and E respectively so that BD=CE.prove thatBE=CD
*April 22, 2012 by majumder*

**math**

in an isosceles triangle ABC ,AB=AC.if AB and AC are produced to D and E respectively so that BD=CE.prove thatBE=CD
*April 26, 2012 by majumder*

**help math**

In triangle ABC, points D,E,F are on sides BC,CA,AB respectively such that AD,BE,CF are angle bisectors of triangle ABC. The linesAD,BE,CF are concurrent at I,the incenter of triangle ABC. If Angle BAC=90, what is the measure (in degrees) of Angle EIF?
*May 28, 2013 by andrew*

**geometry**

how long are the congruent legs of isosceles triangle if its base and altitude to the base are 12cm and 8 cm respectively?
*May 17, 2011 by mike*

**geometry**

how long are the congruent legs of isosceles triangle if its base and altitude to the base are 12cm and 8 cm respectively?
*May 17, 2011 by mike*

**geometry**

how long are the congruent legs of isosceles triangle if its base and altitude to the base are 12cm and 8 cm respectively?
*May 17, 2011 by john *

**Math**

The base of an isosceles triangle is 4x cm long.The altitude to the base is 6cm long.Find the length of a leg of the triangle.
*January 20, 2016 by Kath*

**math**

ABC is a isosceles triangle. Line B extended to D. Prove that <ACD = 90 degree.
*August 18, 2012 by soumi*

**Geometry**

Equilateral triangle ABC and isosceles triangle DBC share side BC. If angle BDC= 34 and BD=BC, what is the measure of angle ABD? I don't know how to solve this questions, can someone guide me through?
*November 26, 2014 by Ana*

**geometry**

Equilateral triangle ABC and isosceles triangle DBC share side BC. If angle BDC= 34 and BD=BC, what is the measure of angle ABD? I don't know how to solve this questions, can someone guide me through?
*November 26, 2014 by Ana*

**geometry**

In isosceles triangle ABC, AB = BC, and D is a point between A and C on AC. Can you conclude MO > ML, MN > MO, angle L > angle BDA, or angle N > angle BDC
*January 5, 2011 by Nick*

**MATHS**

the base BC of a triangle ABC is divided at D so that BD=1/3 BC .prove that ar(triangle ABD)=1/2 ar (triangle ADC)
*March 16, 2013 by BAISHALI*

**Math (Geometry)**

The perimeter of right triangle ABC is equal to the perimeter of isosceles triangle DEF. The lengths of the legs of the right triangle are 6 and 8. If the length of each side of the isosceles triangle is an integer, what is the greatest possible length for one of the sides of ...
*August 7, 2012 by ANONYMOUS*

**geometry**

I need to figure out this proof, the figure is two triangles forming a rhombus. Given: segment BD is the angle bisector of triangle ABC and triangle ADC Prove: Triangle ABD is congruent to Triangle CBD So far I have segment BD is the angle bisector of triangle ABC and triangle...
*December 15, 2013 by cassidy*

**Geometry**

in triangle ABC, BD bisects <ABC, <ABD = 4x + 6 and m<DBC = 5x -5. find the m<abc
*January 1, 2013 by Arooj*

**Math**

In an isosceles triangle, the perimeter is 8 more than 2 times on of the legs. If the perimeter is 28 in, find the length of the base. A. 16 in B. 18 in C. 10 in D. 8 in Given triangle ABC with A(-3, 2), B(-1, -4), and C(4, 1), write the equation for the line containing ...
*January 14, 2016 by SkatingDJ*

**math**

Triangle LNK is isosceles and line LK is the base. use a paragraph proof to prove that triangle LNK is equal to triangle KNM
*May 13, 2013 by emilee*

**math**

in the triangle ABC , AD ray bisects the exterior angle of the triangle at A and intersects CB ray at D . if AB = 6 cm , AC = 8 cm , and BC = 5 cm , find the length of BD line segment
*March 2, 2011 by Hossam Nassar*

**geometry**

The medial triangle of a triangle ABC is the triangle whose vertices are located at the midpoints of the sides AB, AC, and BC of triangle ABC. From an arbitrary point O that is not a vertex of triangle ABC, you may take it as a given fact that the location of the centroid of ...
*April 30, 2013 by denise*

**geometry**

I sent question about rt triangle, ABC, needing to find a & b. altitude was 4, base a and hypotenuse b. You mentioned knowing another angle. There is one < A is 45 degrees. Thanks for all your help. Math is not an easy subject for me.
*April 25, 2015 by robin*

**Geometry HELP**

An isosceles triangle Î”ABC has its altitude at the y-axis and its base at the x-axis. D is the midpoint of segment AC and E is the midpoint of segment CB. Given the coordinates A(-2a, 0), B(2a, 0), and C(0, 2b), determine the coordinates of midpoints D and E. a.)D(2a,-b); E(-...
*June 10, 2010 by Ariel*

**Geometry Help**

1.) An isosceles triangle Î”ABC has its altitude at the y-axis and its base at the x-axis. D is the midpoint of segment AC and E is the midpoint of segment CB. Given the coordinates A(-2a, 0), B(2a, 0), and C(0, 2b), determine the coordinates of midpoints D and E. a.)D(2a,-b...
*June 12, 2010 by Ariel*

**geometry**

In a triangle ABC,E and F are the mid-points of AC and AB respectively. The altitude AP to BC intersects EF at Q.Prove AQ =PB.
*October 29, 2010 by Surendra*

**Algebra**

Triangles ABC and DEF are similar. Find the area of triangle ABC. Round your answer to the nearest tenth. Triangle ABC has a base of 12m. Triangle DEF has a base of 18m and height of 12m
*May 7, 2014 by Barb*

**Agent HELP! Trigonometry**

An isosceles triangle ABC has two sides 17cm in length and a base 10cm in length. Find the size of the angle between the equal sides.
*March 5, 2014 by Jnr John*

**Math**

The two sides of a isosceles triangle have a fixed lenght of 14 cm. The opposite angle at the base of the triangle increases by 0.3 rad/min. a) what is the growth rate dx/dt of the base of the triangle when the opposite angle mesures 1.6 rad? (Use the law of sin) b) What is ...
*April 19, 2011 by Ralph*

**Math**

The two sides of a isosceles triangle have a fixed lenght of 14 cm. The opposite angle at the base of the triangle increases by 0.3 rad/min. a) what is the growth rate dx/dt of the base of the triangle when the opposite angle mesures 1.6 rad? (Use the law of sin) b) What is ...
*April 19, 2011 by Ralph*

**Math**

The two sides of a isosceles triangle have a fixed lenght of 14 cm. The opposite angle at the base of the triangle increases by 0.3 rad/min. a) what is the growth rate dx/dt of the base of the triangle when the opposite angle mesures 1.6 rad? (Use the law of sin) b) What is ...
*April 20, 2011 by Ralph*

**Math**

The two sides of a isosceles triangle have a fixed lenght of 14 cm. The opposite angle at the base of the triangle increases by 0.3 rad/min. a) what is the growth rate dx/dt of the base of the triangle when the opposite angle mesures 1.6 rad? (Use the law of sin) b) What is ...
*April 20, 2011 by Ralph*

**maths**

In triangle ABC angle B > angle C if AM is the bisector of angle BAC and AN perpendicular BC. prove that angle MAN =1/2(angle B - angle C)
*August 23, 2011 by Anonymous*

**Geometry**

Given triangle ABC, AD bisects angle BAC,and AE=ED Prove AE/AC=BD/BC Because I cant draw it I will explain. Its a triangle, A is the point at the top, B is the point at the bottom left and C is the point at the bottom right.There is a line going right down the middle, which is...
*September 29, 2012 by Teisha*

**geometry**

I have triangle XYZ with BX as the bisector sides XY and XZ are congruent. I have to write a proof for angle Y being congruent to angle Z. This is what I have, but it doesn't seem correct - can anyone help? XY is congruent to XZ - Given XB bisects angle XYZ - Perpendicular ...
*December 13, 2009 by josh*

**geometry!!!!!!**

ABC is an isosceles triangle with AB = BC. The circumcircle of ABC has radius 8. Given further that AC is a diameter of the circumcircle, what is the area of triangle ABC?
*February 12, 2013 by please help me out!!! please*

**Math**

Find altitude of isosceles triangle if è=53 degrees (the equal angles) and the base is 8 inches.
*December 2, 2010 by Ro*

**geometry**

triangle ABC is an isosceles right triangle. The endpoints of the hypotenuse of ABC are A(4,7)B(8,1). Find the possible coordinates for the vertex C
*October 23, 2011 by Emily *

**MATHS**

In a triangle ABC, angle B> angle C. If AM is the bisector of angle A and An is perpendicular to BC. Prove that angle MAN=1/2(angle B-angle C).
*June 14, 2015 by AISHA*

**Math. Urgent please help**

ABC is an isosceles triangle. If AB =AC =16, BC=8. D is the midpoint of side AC , and G is the centroid of triangle ABC , find BD .
*December 20, 2013 by Lwint*

**geometry**

6. The isosceles trapezoid is part of an isosceles triangle with a 34° vertex angle. What is the measure of an acute base angle of the trapezoid? Of an obtuse base angle? The diagram is not drawn to scale. (1 point)73o; 107o 34o; 146o 73o; 146o 34o; 107o
*February 13, 2013 by linda*

**geometry**

Find the length of the altitude to the base of an isosceles triangle if the length of one leg is 17 and the base is 16.
*March 7, 2011 by Anonymous*

**Calculus**

Show by vector calculation that the bisector of the angle between the two equal sides of an isosceles triangle bisects the third side and is perpendicular to it.
*May 13, 2012 by Anonymous*

**Geometry **

Line BD bisects angle ABC. Angle ABC= 9x. Angle ABD= 4x+13. Finds angle DBC
*September 23, 2013 by Taylor*

**maths**

the perimeter of an isosceles triangle is 28cm with sides 4y = 6y-2x+1 and base x+2y all in cm .find x and y and hence state the lengths of the sides of the triangle. solution. 4y = 6y-2x+1. ; -2y+2x=1.also altitude = |4y|^2=x^2+ |x+2y|^2 =
*May 11, 2015 by chimere*

**vertex angle**

The three angles add to 180 degrees. Also , the two base angles of the isoscele triangle are equal, .. Set those base angles equal, and solve for x. Put that value of x into the given, and compute the base angles. The third angle will be the amount to add to the two base ...
*August 16, 2007 by Anonymous*

**math**

In a triangle ABC,right angled at B, BD is drawn perpendicular to AC. prove that: (i) angle ABD = angle c (ii) angle CBD = angle A
*July 27, 2012 by sunny*

**geometry**

In a triangle ABC,right angled at B, BD is drawn perpendicular to AC. prove that: (i) angle ABD = angle c (ii) angle CBD = angle A
*July 27, 2012 by sunny*

**Geometric Proofs**

Given: line AB is congruent to line AC, Angle BAD is congruent to angle CAD. Prove: line AD bisects BC Picture: An upside down triangle divided inhalf to form two triangles Angle BAD and angle CAD. They share a common side of AD. and point D bisects line BC. and Angle c and ...
*December 13, 2011 by Tengo anos Cuarenta y uno*

**Geometric Proofs**

Given: line AB is congruent to line AC, Angle BAD is congruent to angle CAD. Prove: line AD bisects BC Picture: An upside down triangle divided inhalf to form two triangles Angle BAD and angle CAD. They share a common side of AD. and point D bisects line BC. and Angle c and ...
*December 13, 2011 by Tengo anos Cuarenta y uno*

**geometry**

Write a flowchart proof: given BD bisects <abc and <1 is congruent to <3 and prove angle 2 is congruent to <3
*November 14, 2012 by sherianna johnson*

**math**

in triangle abc ad is bisector of angle a and angle b is twice of angle c prove that angle bac is equal to 72
*May 11, 2012 by priyanka*