# Question #23c4e

##### 1 Answer

Nov 30, 2016

#cos15˚ = cos60˚cos45˚ + sin60˚sin45˚#

We know, by the special triangles, that

#cos15˚ = (1/2)(1/sqrt(2)) +sqrt(3)/2(1/sqrt(2))#

#cos15˚ = 1/(2sqrt(2)) + sqrt(3)/(2sqrt(2))#

#cos15˚ = (1 + sqrt(3))/(2sqrt(2))#

Hopefully this helps!