Trig help????!!!!?

Question

Okay so I don't understand this.

The problem is to solve the equation in the indicated domain

the equation is :
the cosine 3 theta times the cosine of twelve degrese minus the sine of 3 theta times the sine of twelve degrees equals one half. The domain is fomr -90 to 90 degreese and you have to find the general solution and use the general soltuion to find the critial points within the domain

I really don't understand this so if you could help me that would be great!

Answer 1

Use the sum - difference formula. Your equation becomes:
cos(3θ + 12) = 1/2
3θ + 12 = 60
3θ = 48
θ = 16
3θ + 12 = -60
3θ = -72
θ = -24