Question 428020
How to simplify (1 + cos theta) (1 - cos theta) ?

Use the formula a^2 - b^2 = (a-b)(a+b)

(1 + cos theta) (1 - cos theta) 

= (1)^2 - (cos theta)^2 

= 1 - (cos theta)^2 

= (sin theta)^2 [because (sin x)^2 + (cos x)^2 = 1]

Hope it helps!John10