Step-by-step explanation:
cos(A + B) cos(A − B)
Use angle sum/difference formulas:
(cos A cos B − sin A sin B) (cos A cos B + sin A sin B)
Distribute:
cos² A cos² B − sin² A sin² B
Use Pythagorean identity:
cos² A (1 − sin² B) − (1 − cos² A) sin² B
Distribute:
cos² A − sin² B cos² A − (sin² B − sin² B cos² A)
cos² A − sin² B cos² A − sin² B + sin² B cos² A
cos² A − sin² B
A B C D E F G and L are proportional
and H I J and K are non-proportional.
The additive and subtractive method are opposites of each other, so it is important to know how to do each of them so that you could reverse them if you wanted to.
Step-by-step explanation:
