# Math Help - Why not negative?

1. ## Why not negative?

How should I know not to use a negative value after taking a square root? In the question I might have thought cos x=-(4/5) and sin x=-(3/5).

2. Originally Posted by Stuck Man
How should I know not to use a negative value after taking a square root? In the question I might have thought cos x=-(4/5) and sin x=-(3/5).
Look at the domain x which in this case is the first quadrant.

What is the sign of sine and cos here?