# How do you write the expression cos25^circcos15^circ-sin25^circsin15^circ as a sine, cosine or tangent of an angle?

Jun 5, 2018

cos(40˚)

#### Explanation:

Recall that

$\cos \left(A + B\right) = \cos A \cos B - \sin A \sin B$

Therefore

cos25˚cos15˚ - sin25˚sin15˚ = cos(25˚ + 15˚) = cos(40˚)

Hopefully this helps!