# Maths

if cosA = 4/5; sin <0; cosB = 12/13; 0<B<90, determine sin(A-B)

thanks ... :)

1. 👍 0
2. 👎 0
3. 👁 69
1. The first pairing says that sinA is -4/5

If cosB is 12/13, then sinB is 7/13

Sin(A-B)=CosASinB-SinACosB, right?

1. 👍 0
2. 👎 0
2. yeah that's right, can u go on?

1. 👍 0
2. 👎 0
3. I could, but I wont. However, I will be happy to critique your work or thinking

1. 👍 0
2. 👎 0
4. Error: sinA=-3/5

in all cases, sin^2 Theta + cos^2 Theta=1

1. 👍 0
2. 👎 0
5. well, i got:

(-4/5)(12/13) - (4/5)(7/13)
therefore

(-48/65) - (28/65)

therefore:

1. 👍 0
2. 👎 0
6. from if cosA = 4/5; sin <0 we know that A is in the fourth quadrant and sinA = -3/5

from cosB = 12/13; 0<B<90 we know sinB = 5/13

sin(A-B) = sinAcosB - cosAsinB
= (-3/5)(12/13) - (4/5)(5/13)
= -56/65

1. 👍 0
2. 👎 0
posted by Reiny
7. change the Sin A in the first term, and it works.

1. 👍 0
2. 👎 0
8. i knew that was wrong, coz my answer should be in the 50's haha..thanks though, great help

can i ask how you got sinA and sinB with that information :)

no point in me just copying it i would like to know how you got it

1. 👍 0
2. 👎 0
9. In any angle, the sum of the squares of the cosines and sines is equal to one. Use that to solve.

1. 👍 0
2. 👎 0

## Similar Questions

1. ### Trigonometry

I need to prove that the following is true. Thanks. csc^2(A/2)=2secA/secA-1 Right Side=(2/cosA)/(1/cosA - 1) = (2/cosA)/[(1-cosA)/cosA] =2/cosA x (cosA)/(1-cosA) =2/(1-cosA) now recall cos 2X = cos^2 X - sin^2 X and we could say

asked by Dirk on April 17, 2007
2. ### math (trig)

i have some problems doing trig the first one is: Show that cos(x/2) sin(3x/2) = ½(sinx + sin2x) i know that you are supposed to substitute all those trig function things in it but i kind of forgot how to the only that i can see

asked by jacob on April 30, 2007
3. ### MathsSs triG

Consider sin(x-360)sin(90-x)tan(-x)/cos(90+x) 1.A.SIMPLIFY sin(x-360)sin(90-x)tan(-x)/cos(90+x) to a single trigonometric ratio B.hence or otherwise without using a calculator,solve for X if 0

asked by katlego ratsoma on October 3, 2013
4. ### further mathematics

Let P=(cosA sinA) (sinA cosA) Q=(cosB sinA) (sinB cosA) show that PQ=(cosA(A-B) sin(A B)) (sinA(A B) cos(A-B))

asked by James on September 17, 2013
5. ### 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
6. ### trig

How to do this one? (sina/1-cosa) + (1-cosa/sina) = Also, wanted to ask if I did another one right: 1 - sin^2a + tg^2a * cos^2a = 1 - sin^2a + (sina/cosa)^2 * cos^2a = 1 - sin^2a + sin^2a = 1 ???

asked by Evelina on November 12, 2011
7. ### trigonometry

x×sin^3A=y , cos^3A = sinA × cosA , x×sinA= y×cosA , then prove that x^2+ y^2= 1 I have no idea

asked by Venkatesh on March 23, 2016
8. ### Trig

I don't know the physics behind Snell's Law, but I can do the math Snell's Law says sin(angle of incidence)/sin(angle of reflection) = refractive index since you know the two angles... sin45/sin27 = refractive index =1.5575365 so

asked by Reiny on April 19, 2007
9. ### Precal

I do not understand how to do this problem ((sin^3 A + cos^3 A)/(sin A + cos A) ) = 1 - sin A cos A note that all the trig terms are closed right after there A's example sin A cos A = sin (A) cos (A) I wrote it out like this 0 = -

asked by Joe on January 14, 2010
10. ### trigonometry

tanA - sin A /sin^2A= tan A / 1 + cosA Please prove this

asked by Venkatesh on March 22, 2016
11. ### Physics

physics - drwls, Sunday, January 24, 2010 at 2:50am Compute the angle of the strings from vertical. It is sin^-1 (8.5/40) Call this angle A If the string tension is T T sin A = F (the Coulomb force) T cos A = M g tan A = F/Mg You

asked by Lanise on January 25, 2010

More Similar Questions