# If cosθ = -5/13 and 0 <= θ <= 2π, what are possible values of θ?

1. Nov 4, 2013

### Ace.

1. The problem statement, all variables and given/known data

If cosθ = -5/13 and 0 <= θ <= 2π, what are possible values of θ?

2. Relevant equations

3. The attempt at a solution
θ is in quadrant 2 or 3

related acute = cos$^{-1}$(5/13)
= 1.18
θ = π - 1.18

related acute angle = 1.18
θ = π + 1.18

Those are the two values I got for θ. But my book says the answer is 5.14. Can you tell me where I am going wrong?

2. Nov 4, 2013

### Mentallic

Where didn't you go wrong???

Nah, I'm just kidding The book's answer is wrong, you're right. They accidentally included the angle in the 4th quadrant rather than the 3rd as you've correctly done.