Question

PLEASE HELP :)

Express the following as a function of a single angle.
cos 40 cos 70 + sin 40 sin 7

The answer is going to be cos [ ? ] degrees .

Answer 1

cosA.cosB +sinA.sinB= cos (A-B)

A=40 , B= 70

cos 40 cos 70 + sin40 sin70= cos (40-70)

=cos(-30)

=cos(30)

=3^.5/2 (square root of 3/2)