Multiply then use fundamental identities to simplify the expression below and determine which of the following is not equivalent (2 - 2cos x)(2 + 2cos x)

Question

a.4 - 4cos^2 x
b . 4 - cos^2 x
c.4/(1 + cot^2 x)
d. 4sin^2 x
e.4/(csc^2 x)

Answer 1

recall that (a-b)(a+b) = a^2-b^2
so, 2^2 - (2cosx)^2 = 4 - 4cos^2x = 4(1-cos^2x) = 4sin^2x

only B is not equivalent to that