Find cos θ if sin θ = - (5/13) and tan θ > 0

Remember:

sin²x + cos²x = 1

(-5/13) ² + cos² θ = 1

(25/169) + cos² θ = 1

cos² θ = 1 - (25/169)

cos² θ = (144/169)

tan θ > 0 ⇒ cos θ = negative

cos θ = - √ (144/169)

cos θ = - (12/13)