Question

Which expression is equivalent to (sin x + 1)(sin x − 1)?

Answer 1

A. cos2xB. -cos2xC. cos2x + 1D. cos2x − 1E. -cos2x + 1

Answer 2

You have to remember that (a+b)(a-b)=a^2 - b^2. Then work out the answer using the trig identity sin^2x + cos^2x = 1.

Answer 3

So D.?

Answer 4

Is D equivalent to sin^2x-1? What happens if you start with sin^2x + cos^2x = 1 and change it around by subtracting 1 from each side and then substracting cos^2x from each side?