Thread: Identities

Stuck on a exm revision question please help, the question is:

Find the exact value of:
a) cos(x) if sin(x) =12/13 and 90°<x<180°
b) sin(x) if cos(x) =-3/2 and x is in the third quadrant
c) cos(x) if sin(x) =-7/25 and x is in the fourth quadrant
d) sin(x) if cos(x) = (root 3)/2 and 3pi/2<x<2pi



thnx i dont know how t use ths very well i hope you understand what i mean

a) Use the Pythagorean Identity and remember that cosine is negative in the second quadrant.

b) Use the Pythagorean Identity and remember that in the third quadrant, both sine and cosine are negative.

c) Use the Pythagorean Identity and remember that cosine is positive in the fourth quadrant.

d) Use the Pythagorean Identity and remember that sine is negative in the fourth quadrant.