Saturday
December 3, 2016

Posts by Reiny

Total # Posts: 36,897

Calculus
Make a sketch of the cross-section let the radius be r, let the vertex angle be 2Ø we have a right-angled triangles with angle Ø, opposite is r, and adjacent is 12 tanØ = r/12 12tanØ = r 12 sec^2 Ø (dØ/dt) = dr/dt when r = 6 , ...
August 30, 2016

math homework help
the major axis lies along the y-axis, so a^2 + 4^2 = 7^2 a^2 = 33 a=√33 x^2/33 + y^2/49 = 1
August 30, 2016

Rainy can you help me with this question?!
just look at the numbers in the corresponding positions x y 1 9 = 3 5 1 9 so x=3 and y=5
August 30, 2016

math homework help
If f(x) = 5-2x lim f(x+h) - f(x) / h = lim (5 - 2(x+h) - 5 + 2x)/h = lim (5 - 2x - 2h - 5 + 2x)/h = lim (-2h)/h = -2
August 30, 2016

Maths
(1/2)x - 1/3 = 4 times 6 , the LCD 3x - 2 = 24 3x = 26 x = 26/3 check: 1/2 of 26/3 = 13/3 difference between 13/3 and 1/3 = 12/3 or 4 we are good here.
August 30, 2016

maths
I will assume your first equation has a typo, then y = 16-x plug into the 2nd x^2 + (16-x)^2 = 128 2x^2 - 32x +128 = 0 x^2 - 16x + 64 = 0 (x-8)^2 = 0 take over, compare your answer to http://www.wolframalpha.com/input/?i=plot+x%2By%3D16,++x%5E2+%2By%5E2+%3D128
August 30, 2016

math
Straightforward trig ratio tan Ø = opposite/adjacent tan 40° = height/500 height = 500tan40° = ......
August 30, 2016

calculus
recall area of parallelogram using vectors u and v = | u X v| go for it, you have u = (-2,1,5) and v = (4,-3,-3)
August 30, 2016

calculus
if by v * w , you mean v X w , the cross product, then v X w = (5, 8, -1) X (-2, 8, 3) = (32, -13, 56) , I assume you know how to find the cross-product Then u . (v * w) = (5, 9, -6) . (32, -13, 56) = 160 - 117 - 336 = - 293
August 30, 2016

math
does it look like this ? (9493) ? Are you studying numbers with different bases?
August 30, 2016

math
What does (94) 93 mean? check your typing.
August 30, 2016

mzumbe
the difference between 7th and 5th terms is 192 ---> ar^6 - ar^4 = 192 ar^4(r^2 - 1) = 192 ** the difference between 15th and 3rd terms is 48 ---> ar^14 - ar^2 = 48 ar^2(r^12 - 1) = 48 *** divide ** by *** r^2(r^2 - 1)/(r^12 - 1) = 4 **** r^4 - r^2 = 4r^12 - 4 4r^12 - r^...
August 30, 2016

Measurements and applications
50 mm ----> 4 km 1 mm ------> 4/50 km 75 mm ----> (75)(4/50) km or 6 km ratio = 50 mm : 4 km = 50 mm : 4000000 mm = 1 : 80,000 c) "48squared" km? from your given: (4 km)^2 ---> (50 mm)^ 16 km^2 = 2500 mm^2 1 km^2 = 2500/16 mm^2 48 km^2 = (48)(2500/16) mm^...
August 30, 2016

math
Use Venn diagrams draw two intersecting circles , one labeled E and the other labeled H within a rectangle. You know the intersection of E and H is 70 and the part outside the two circles is 8 It said 5 failed in H only, so they must have passed E, so they can't be part of...
August 30, 2016

Math
since (8,6) lies on it, 8/a - 6/b = 1 (8b - 6a)/(ab) = 1 8b - 6a = ab 8b - ab = 6a b(8 - a) = 6a b = 6a/(8-a) ** x/a - y/b = 1 is in the intercept form, that is the x-intercept is (a,0) the y-intercept is (0,b) so the area of the triangle is (1/2)(ab) (1/2)(ab) = 12 ab = 24...
August 29, 2016

Math
the LCD is 3(3x-9), so let's multiply both sides by that 3(5x+6) = 7(3x-9) this is often called "cross-multiplying" 15x + 18 = 21x - 63 -6x = - 81 x = -81/-6 = 13.5
August 29, 2016

Math
ambiguous. did you mean the way you typed it, or (5x+6)/(3x-9)=7/3 or 5x+6/(3x) -9=7/3 or .. ?
August 29, 2016

Geometry
fg = ? but you said fg = 15x-9 check your typing
August 29, 2016

Math
remember f(x) is just another name for the y value of a function so y = -f(x) means that whatever the y value was of the original function, in - f(x) it is simply the opposite. Thus you have a reflection in the x-axis y = 2 f(x) - 1 we are stretching the y value by a factor of...
August 29, 2016

algebra
2x - 4 = 22 and 2x - 4 = -22 I assume you know how to solve these
August 29, 2016

Math
(1/4)g = 16 ---> g = 64 (1/8)b = 7 ---> b = 56 finish it up
August 29, 2016

math
done, look under Related questions below
August 29, 2016

math
" .... and ones digits are greater than 10 digits" makes no sense to me
August 29, 2016

Maths
solve for x .8x = 15
August 29, 2016

math
hint: from x+y = 16 ----> y = 16-x sub that into the 2nd equation and solve for x using your method of solving quadratics let me know what you get
August 29, 2016

math
What do you know about the values of a, b, and c in a hyperbola?
August 29, 2016

math
"and the distance between the centre between F and F, and the semi-ellipse is 5 meters. " ---> confusing, but I think I figured it out Use the properties of an ellipse in terms of its values of a, b, and c c = 14 b = 5 a = ?? In a standard ellipse, a^2 = c^2 + b^2...
August 29, 2016

maths
length ---- x width = x-4, (it said so) b) perimeter = all the way around = 2x + 2(x-4) = ..... , simplify it c) set your expression from b) equal to 20 and solve for x
August 29, 2016

MATH
Make a sketch. Think of the plant as a radius of a circle the plant would draw out. Draw in a horizontal to show the lake. At the vertical let OP be the length of the plant, O is the centre and P at the top. then draw a horizontal 6 cm below P so the plant touches at A and B. ...
August 29, 2016

radical equation please help!!!
your original thinking that sqrt(1+x) -sqrt(1-x) = sqrt (1-x-sqrt(1+x)) is incorrect test it with a value of x e.g. suppose x = .5 then you would have √1.5 - √.5 = √(1 - .5 + √1.5 ) or appr .5176 = appr .455 , not even close What was the rest of the ...
August 29, 2016

math
1/4 of 48 = 12 1/6 of 48 = 8 1/8 of 48 = 6 so far we counted 26 The remaining 22 must be green
August 29, 2016

math help please?!
Argghhh, hard to read, besides, you appear to have a typo near the end 1/6 x = 1/8 y - z = -24 -----> 1/6 x + 1/8 y - z = -24 did you mean: 1/3 x + 3/4 y - 2/3 z = -8 x + 1/2 y + 1/3 z = 18 1/6 x + 1/8 y - z = -24 ?? if so , I would clean them up first, 1/3 x + 3/4 y - 2/3 ...
August 29, 2016

math help please?!
subbing in your values, you will end up with 3 equations, in 3 unknowns #1. 161 = 12a + v + c , I will use c to avoid confusion with a second s #2. 98 = 48a + 2v + c #3. 3 = 108a + 3v + c #3 - #2 ------> 60a + v = -95 #2 - #1 ------> 36a + v = -63 subtract those two ... ...
August 29, 2016

math
number of pieces --- x she sold 2/3 of them, leaving (1/3)x gave half of that , or (1/6)x to friends, leaving her with (1/6)x but (1/6)x = 6 x = 36 It was cut into 36 pieces
August 29, 2016

math
Answered when you were Rose
August 29, 2016

Math
rates of change is the slope of the line the slope of the first line is 2 the slope of the second line is 1/4 The larger the slope, the greater the rate of change, so what do you think?
August 28, 2016

maths
2 by 2/3 ---> old way of saying 2 divided by 2/3 as in 12 ÷ 3 or 12 by 3 (don' know why they didn't just say 3)
August 28, 2016

Math
number of people --- x (5/7)x = 540 x = 540(7/5) = ...
August 27, 2016

Little flowers convent school
So which is it, without leaving any margin, or leaving a margin of 1.5 m all around ? What is the size of the tile ?
August 27, 2016

percentage
original cost per apple ---- x reduced cost per apple = (2/3)x = 2x/3 75/(2x/3) - 75/x = 25 225/(2x) - 75/x = 25 times 2x 225 - 150 = 50x 50x= 75 x = 75/50 = 1.5 The original price is 1.5 and the reduced price is (2/3)(1.5) = 1 check: at 1.5 Rs, he can buy 75/1.5 or 50 apples ...
August 27, 2016

Math
40 : 60 : 120 : 140 = 4 : 6 : 12 : 14 = 2 : 3 : 6 : 7
August 26, 2016

value
from what you have: Logx + logy=4 logx +2logy=3 log(xy) = log(x^4 y^2) = 3 so : log(xy) = log(x^4 y^2) x^4 y^2 = xy x^3 y = 1 y = 1/x^3 , of course x > 0 in logx + logy = 3 logx + log(1/x^3) = 3 log(x(1/x^3)) = 3 log (1/x^2) = 3 1/x^2 = 10^3 = 1000 1000x^2 = 1 x^2 = 1/1000 ...
August 26, 2016

maths reiny help!!
I just copied my previous solution and changed the numbers: Suppose that the cost of each of the original books was $x per book So the cost was 80x He got a 15% discount, so the cost was (.85)80x = 68x but for 68x he actually got 90 books so the cost of each book was only 68x/...
August 26, 2016

algebra
width ---- w length ---- w+6 width*length = area w(w+6) = 72 w^2 + 6w - 72 = 0 (w-6)(w+12) = 0 w = 6 or w = a negative the width is 6 cm with only a few nice choices you could have easily checked each one in your head e.g. for the first one: is 10 times 16 equal to 72 ? NO etc
August 26, 2016

Math
cows --- x chickesn --- y x+y = 12 ** 4x + 2y = 28 or 2x + y = 14 *** subtract ** from *** x = 2 then y = 10 2 cows and 10 chicks
August 26, 2016

math
2 workers takes 15 hours to make 3 fireplaces 2 workers takes 5 hours to make 1 fireplace 2 workers takes 20 hours to make 4 fireplaces 1 worker takes 40 hours to make 4 fireplaces 5 workers takes 8 hours to make 4 fireplaces or it takes 30 work-hours to make 3 fireplaces it ...
August 26, 2016

Maths
let Katie's present age be k let Melanie's present age be m Five years ago: Katie ---- k - 5 Melanie -- m-5 k-5 = 10(m-5) k - 10m = -45 ** 2nd condition: Katie's age in 15 years = 3(Melanies age in 11 years) k + 15 = 3(m + 11) k+15 = 3m + 33 k - 3m = 18 *** ...
August 25, 2016

MAth
I did this for you yesterday http://www.jiskha.com/display.cgi?id=1472041460 Why are you repeating it? btw, it should say "How many complete revolutions are needed?"
August 25, 2016

Math help
recall that cot^2 x +1 = csc^2 x so ∫(cot⁡^2 x-csc^2 x)^2dx = ∫(cot⁡^2 x-(cot^2 + 1)^2dx = ∫ -1 dx take over
August 25, 2016

MATHS
what is 1 - .8(.7) ?
August 25, 2016

Math
add 246 to both sides
August 24, 2016

Math
correct
August 24, 2016

Math
Since a constant multiplier is not usually written behind a binomial, I suspect you meant: (x+1)^2 = 9 then x+1 = ±√9 = ±3 x+1 = 3 ----> x = 2 or x+1 = -3 ---> x = -4
August 24, 2016

MAV school
x/4 + (120-x)/5 = 28 times 20 , the LCD 5x + 4(120-x) = 560 5x + 480 - 4x = 560 x = 80 so we split them up as 80 and 40 , with the 80 being divided by 4 and the 40 divided by 5 check: 80/4 + 40/5 = 20+8 = 28
August 24, 2016

MAth
Circumference of barrel = 56π cm number of rotations = 2944/(56π) = appr 16.7
August 24, 2016

MATHS PLZZ HELP PLZZ SOMEONE KINDA BEG YOU
Suppose that the cost of each of the origininal bools was $x per book So the cost was 50x He got a 10% discount, so the cost was (.9)50x = 45x but for 45x he actually got 60 books so the cost of each book was only 45x/60 = 3x/4 As a percentage: (3x/4) / x = 3/4 or 75% which ...
August 24, 2016

math
The assumption would be that he would be randomly guessing at the answer. Since 12/15 = .8, why did you not include the probability of getting 12 correct out of the 15 ? Try adding that to your other cases. For b) wouldn't getting 20 out of 25 correct yield 80% ? Same for ...
August 24, 2016

Math
clearly I have a typo in the 3rd last line, should be = 2^2011 (-√3/2 + (1/2) i )
August 24, 2016

Math
let's use De Moivre's Theorem let z = √3 - 1 sketching it in the Argand plane will give you |r| = 2, and tanØ = -1/√3 Ø = 330° or 11π/6 z = 2(cos 330° - i sin 330°) z^2011 = 2^2011(cos (663630°) - i sin(663630°) ) ...
August 24, 2016

Math
By "a complete sketch" they very likely want a right-angled triangle. since tanØ = opposite/adjacent = 3/4 and the angle is in the third quadrant y = -3 and x = -4 r^2 = 9 + 16 = 25 r = 5 sin Ø = -4/5 cos(Ø + 180) = cosØcos180 - sinØ...
August 23, 2016

Maths
circumference of wheel = πd = .98π metres number of rotations = 1540 m/.98π m = 531.898.. = appr 532 rotations how did you get 500?
August 23, 2016

Maths
I will assume that you meant: (cosecθ-cotθ)^2=(1-cosθ)÷(1+cosθ) or else the identity is not true. LS = (1/sinØ - cosØ/sinØ)2 = (1-cosØ)^2 / sin^2 Ø = (1 - cosØ)(1-cosØ)/( (1 - cosØ)(1 + cos&...
August 23, 2016

math
What is 1.74 / 0.29 ?
August 23, 2016

Math
width or breadth ----- x cm length --------------- 3x - 2 solve for x, and sub back into my definitions 2x + 2(3x-2) = 60
August 23, 2016

statistics
number of "not reds" is 20 so prob(not red) 20/26 = 10/13 or prob(red) = 6/26 = 3/13 prob(not red) = 1 - 3/13 = 10/13
August 23, 2016

math
(3^-3)x = 4 (1/3^3)x = 4 (1/27)x = 4 x = 108
August 23, 2016

Correction - Maxwell
How did you get your answer? It is not correct Felicia's present age .... f Tom's present age ........ t 3f = t+4 ** f+3 + t+3 = 30 f+t = 24 t = 24 - f *** sub *** into ** 3f = 24-f + 4 4f = 28 f = 7 then t = 24-7 =17 Felicia is now 7 and Tom is now 17 check: three ...
August 23, 2016

Math
If exterior angle is 50°, then each interior angle is 130° let the number of sides be n , where n is a whole number sum of interior angles = 180(n-2) each interior angle is 180(n-2)/n 180(n-2)/n = 130 180n - 360 = 130n 50n = 360 n = 7.2 , silly answer, so nope, not ...
August 22, 2016

Math
slope of a line is the tangent of the angle that the line makes with the horizontal, so slope = rise/run = 225/1000 = 9/40 so the hypotenuse of the corresponding triangle is √(40^2 + 9^2) = √1681 cosine (angle) = 40/√1681 = 40/41
August 22, 2016

Math
unit digit of original number ---- x tens digit of original number ---- x+5 original number = 10(x+5) + x = 11x + 50 number reversed = 10x + (x+5) = 11x + 5 11x+50 + 11x + 5 = 99 22x = 44 x = 2 the original number was 72 check: 72 + 27 = 99 , my answer is correct
August 22, 2016

Math
well, |-9| = 9 so you have -9/9 = -1
August 21, 2016

Math
you got it 7 - √11
August 21, 2016

Algebra
I assume you meant: |t-2| = -1 since by definition |anything| is never negative, there is no solution.
August 21, 2016

math
Ok, who is stopping you ?
August 21, 2016

math
each of the other equal sides ---- x cm x^2 + x^2 = 98^2 2x^2 = 9604 x^2 = 4802 x = √4802 = 49√2 cm
August 21, 2016

theory of probability
What you have is the total number of ways to place the caps Let's actually list them, there are only 6 I will write them as a pair of digits, where the first number is the bottle and the second digit is the cap 11 22 33 ----> all correct 11 23 32 ----> 1 right, 2 ...
August 21, 2016

Maths Percentage
(1.25x)(r) = x 1.25r = 1 r = 1/1.25 = .8 = 80% So it must be reduced by 20% check: suppose the original was $100 after the increase it would be 125 after a reduction of 20% is would be .8(125) = 100
August 21, 2016

Math
2000(1+i)^2 = 24200 (1+i)^2 = 1.21 take √ of both sides, etc
August 21, 2016

please help with this trigonometric identity!
I am sure that you meant: (cos 'a' - cos 'b') / (sin 'a' + sin 'b') + (sin 'a' - sin 'b') / (cos 'a' + cos 'b') = 0 the LCD is (sina + sinb)(cosa + cosb) LS = ( (cosa - cosb)(cosa + cosb) + sina - sinb)(sina - ...
August 19, 2016

Maths Algebra
3(5x-7)-2(9x-11)=4(8x-13)-17 15x - 21 - 18x + 22 = 32x - 52 - 17 -35x = -70 x = 2 check: LS = 3(10-7) - 2(18-11) = 9 - 14 = -5 RS = 4(16-13) - 17 = 12 - 17 = -5 my answer is correct
August 19, 2016

Maths Squares and Square roots
The sum cannot be found without some kind of addition somewhere, but .... look at the last one: add the first and last ---> 22 add the 2nd and 2nd last ---> 22 add the 3rd and 3rd last ----> 22 how such pairs of 22 can you find? If you have an odd number of terms, do ...
August 19, 2016

Maths Triangles
Too messy to type here. That proof should be in most textbooks, if not, Google it. https://search.yahoo.com/search?fr=spigot-nt-gcmac&ei=utf-8&ilc=12&type=692858&p=proof%20:%20sum%20of%20angles%20in%20a%20triangle%20equals%20180
August 19, 2016

Maths Quadrilaterals
Once you have proven that the sum of the angles in a triangle is 180° ..... in your quad, draw in any diagonal to create two triangles. So ......
August 19, 2016

Maths Time and Work
Poorly worded. By "rates of working" , do you mean the amount of work done, or the time taken to do the same job.
August 19, 2016

Maths Unitary Method
The key word in the first part is "or" men's rate = 875/5 = .. women's rate = 875/7 = ... then 10(men's rate) + 7(women's rate) = ... (politically incorrect question)
August 19, 2016

Maths Percentage
what is 54000/1.1 ?
August 19, 2016

Maths Compound Interest
count = 512000(1.025)^2 = .....
August 19, 2016

Maths Compound Interest
When is 1000(1.10)^n = 1331 ? 1.1^n = 1.331 take log of both sides, and use log rules n log 1.1 = log 1.331 n = log 1.331/log 1.1 = .... you do the button pushing
August 19, 2016

geometry
Well, you know that that the area of a triangle = (1/2)bh, where b is the base and h is the height but you are told that h = 3b , so area = (1/2)(b)(3b) 27 = (1/2)(3b^2) times 2 54 = 3b^2 b^2 = 18 b = √18 or 3√2 ft base = 3√2 ft and the height is 9√2 ft...
August 19, 2016

Correction - Maths
I obviously got x = 360 So there are 360 marbles, I have no idea where I got the 510 from, and then I copied it again at the end. Time for my third cup of coffee.
August 19, 2016

Maths
let the total be x (2/5)x = r , also b+54 = (2/5)x b = 2x/5 - 54 = (2x - 270)/5 b : y = 5 : 7 5y = 7b y = (7/5)b y = 7(2x-270)/25 so 2x/5 + (2x-270)/5 + 7(2x-270)/25 = x times 25 10x + 10x - 1350 + 14x - 1890 = 25x -9x = -3240 x = 360 we have 510 marbles check: red = (2/5)(360...
August 19, 2016

math
I had done this for you. http://www.jiskha.com/display.cgi?id=1471418592
August 17, 2016

Analytic Geometry
Since you know the vertex, your equation must be x = a(y-0)^2 + 0 , if the axis of symmetry is horizontal x = ay^2 but (3,5) lies on it, so 3 = a(25) a = 3/25 x = (3/25)y^2 or 25x = 3y^2
August 17, 2016

Maths
cos(A+B) = cosAcosB - sinAsinB apply it to your question
August 17, 2016

Math
log3 9^4 = 4 log3 9 = 4(2) = 8 or , just think it through 9^4 = 3^8 so log3 3^8 must be 8
August 17, 2016

math
first number --- x 2nd number ---- 1/x x + 1/x = 3 x^2 + 1 = 3x x^2 - 3x + 1 = 0 using competing the square: x^2 - 3x + 9/4 = -1 + 9/4 (x + 3/2)^2 = 5/4 x + 3/2 = ± √5/2 x = -3/2 ± √5/2 x = (-3 + √5)/2 or x = (-3 - √5)/2
August 17, 2016

Math
assuming that "a" is the base - log a x^6 y^7 = -(loga x^6 + loga y^7) = -(6loga x + 7loga y) = -6loga x - 7loga y none of your choices are correct, unless there is a typo with that minus sign
August 17, 2016

Math3c
Just use the definitions of an AP and translate the English to Math. "the sum of the first three terms" = a + a+d + a+2d = 3a + 3d "the sum of the next four terms" = a+3d + a+4d + a+5d = 3a + 12d given: "the sum of the first three terms is one half the...
August 17, 2016

Pre Cal
Show me your expansion, and I will check it. Did you remember that i^2 = -1 ?
August 17, 2016

Pre Cal
take a look at this question I did several years ago http://www.jiskha.com/display.cgi?id=1315862859
August 17, 2016

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