# trig

If sin = 4/5 with A in QII, and sin B = -3/5 with B in QIV find cos(A-B)

1. 👍 0
2. 👎 0
3. 👁 119
1. cos(A-B)= cosAcosB+sinAsinB

If sinA = 4/5 in QII
draw you triangle in QII, and find the third side.
The third side is 3. (Do the same thing for sin B= -3/5
Plug in:
cosAcosB-sinAsinB
=(-3/5)*(4/5)+(4/5)*(-3/5)
=(-12/25) -(-12/25)
=-24/25

1. 👍 0
2. 👎 0
posted by ^Quen^
2. 53. the longest side is 55 cm. find the length of the shortest side

1. 👍 0
2. 👎 0

## Similar Questions

1. ### TRIG!

Posted by hayden on Monday, February 23, 2009 at 4:05pm. sin^6 x + cos^6 x=1 - (3/4)sin^2 2x work on one side only! Responses Trig please help! - Reiny, Monday, February 23, 2009 at 4:27pm LS looks like the sum of cubes sin^6 x +

asked by hayden on February 23, 2009
2. ### trig

If sin A= 1/4 and sin B= -1/2, with A in QII and B in QIV, find tan(A+B)

asked by Chase on April 5, 2012
3. ### tigonometry

expres the following as sums and differences of sines or cosines cos8t * sin2t sin(a+b) = sin(a)cos(b) + cos(a)sin(b) replacing by by -b and using that cos(-b)= cos(b) sin(-b)= -sin(b) gives: sin(a-b) = sin(a)cos(b) - cos(a)sin(b)

asked by Pablo on November 26, 2006
4. ### Calculus

Consider the function f(x)=sin(1/x) Find a sequence of x-values that approach 0 such that (1) sin (1/x)=0 {Hint: Use the fact that sin(pi) = sin(2pi)=sin(3pi)=...=sin(npi)=0} (2) sin (1/x)=1 {Hint: Use the fact that sin(npi)/2)=1

asked by George on September 9, 2008
5. ### Calculus

Consider the function f(x)=sin(1/x) Find a sequence of x-values that approach 0 such that (1) sin (1/x)=0 {Hint: Use the fact that sin(pi) = sin(2pi)=sin(3pi)=...=sin(npi)=0} (2) sin (1/x)=1 {Hint: Use the fact that sin(npi)/2)=1

asked by George on September 9, 2008
6. ### algebra

Can someone please help me do this problem? That would be great! Simplify the expression: sin theta + cos theta * cot theta I'll use A for theta. Cot A = sin A / cos A Therefore: sin A + (cos A * sin A / cos A) = sin A + sin A = 2

asked by Valerie on February 18, 2007
7. ### Calculus

Use a Riemann sum with n = 3 terms and the right endpoint rule to approx. ∫(1, 2) sin(1/x)dx. My teacher just needs the terms written out, no need to add or multiply. This is a problem she did up on the board, so here's her

asked by Justin on November 4, 2015
8. ### Trigonometry

Solve the equation for solutions in the interval 0

asked by Renee on March 7, 2016
9. ### Calculus

Consider the function f(x)=sin(1/x) Find a sequence of x-values that approach 0 such that sin (1/x)=0 sin (1/x)=1 sin (1/x)=-1 Is sin sin (1/x)=0 and sin (1/x)=-1 does not exist. What is sin (1/x)=1 then.

asked by George on September 8, 2008
10. ### Maths

Question : Integrate [x/(1+(sin a*sin x))] from 0 to pi My first thought was to apply integrate f(x) dx= f(a-x) dx method Which simplified the integral into; 2I = integrate [pi/(1+(sin a*sin x))] dx , cancelling out x Then I made

asked by Ashley on March 18, 2019

More Similar Questions