Thursday

December 18, 2014

December 18, 2014

Posted by **stranger** on Monday, April 8, 2013 at 8:49am.

- Geometry -
**Reiny**, Monday, April 8, 2013 at 10:38amJoin the diagonals

Since B - 60° and AB = BC = 21

ABC must be equilateral and AC = 21

Now in triangle ACD we have 3 sides, and by the cosine law I found angle D to be 120°

interesting!

using the sine law in triangle ACD

sin CAD/15 = sin60/21

sin CAD = .61858..

angle CAD = 38.3232... (I stored that)

angle BAD = 60 + 38.32... = 98.21..°

by the cosine law:

BD^2 = 21^2 + 9^2 - 2(21)(9)cos BAD

= 528

BD = √528 or appr 22.98

- Geometry -
**Finalhero**, Wednesday, April 10, 2013 at 4:27pmReiny in the last step u have done an error as 21^2 =441 + 9^2 = 81 = 522

and 2*21*9*cos(98) = - 54.6

so 522 - (-54.6)=522+52.6=574.6

and square root of 574.6 = 23.97 ~ 24

**Answer this Question**

**Related Questions**

geometry - ABCD is a convex quadrilateral satisfying AB=BC=CD,AD=DB and ∠...

geometry...TRIANGLE - ABCD is a quadrilateral with ∠ADC=∠ACD, ∠...

geometry - ABCD is a quadrilateral with ∠ADC=∠ACD, ∠ACB=∠...

Math (Geometry) - ABCD is a parallelogram with side lengths AB=15,BC=10 and &#...

geometry(triangle) - Triangle ABC is a right triangle with ∠ABC=90∘...

maths - ABCD is a convex cyclic quadrilateral such that AB=AD and ∠BAD=90...

maths - ABCD is a convex cyclic quadrilateral such that AB=AD and ∠BAD=90...

simple GEOMETRY!! - In triangle ABC, ∠ABC=30∘,∠ACB=60∘. ...

geometry - ABCD is a rectangle. On line segment AB, E is a point such that &#...

geometry! - ABC is an acute angle triangle with points D and E on BC and AC, ...