Which sum or difference identity could be used to prove that cos(270degrees-feta)=-sinfeta is an identity?

cos (270° - θ) = -sinθ

Step-by-step explanation:

Explanation:-

Trigonometry sum or difference formula

Cos (A+B) = cos A cos B - sin A sin B

Cos (A+B) = cos A cos B + sin A sin B

Given cos (270° - θ) = cos 270° cosθ + sin 270° sinθ

Cos 270° = cos (180°+90°) = -cos 90° = 0

sin 270°   = sin (180°+90°) = -sin 90° = -1

now

cos (270° - θ) = cos 270° cosθ + sin 270° sinθ

cos (270° - θ) = (0) cosθ + (-1) sinθ = -sinθ

Final answer:-

cos (270° - θ) = -sinθ