Question

If cos(θ) equals 4/5 and the angle θ is in Quadrant IV, what is the value of sin(θ)?
(5 points)
5/3
-4/5
-3/5
3/

Answer 1

Use sin^2θ = 1 − cos^2θ = 1 − (4/5)^2 = 1 − 16/25 = 9/25, so sinθ = ±3/5. In Quadrant IV sine is negative, so sinθ = −3/5.