Question

Suppose θ is in the interval (180°, 225°). Find the sign of each function value.

a) Cos(2θ)
b) tan(θ-90°)
c) sin(θ/2)

Answer 1

a) 2A puts you in 1st quadrant --> cos(2A) is positive

b) A-90 puts you in 2nd quadrant --> tan(A-90) is negative

c) A/2 puts you in 2nd quadrant --> sin(A/2) is positive

Answer 2

How do you get to that? Is there any mathmatics behind it that will help me associate it so I can repeat this?

Answer 3

this (rough) diagram should help\