Question

find the exact value of cosine theta given that sin theta equals -12/13 and theta is in the quadrant three

Answer 1

cos θ = -5/13

Explanation:

sin θ = -12/13

Use Pythagorean identity.

sin²θ + cos²θ = 1

(-12/13)² + cos²θ = 1

144/169 + cos²θ = 1

cos²θ = 25/169

cos θ = ±5/13

θ is in the 3rd quadrant, so cos θ < 0.

cos θ = -5/13