Question

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

a. 1+2sinxcosx

b. sec^2x−tan^2x+2cosxsinx

c.sec x + 2 sin x/sec x

d. sin^2x+cos^2x

e. 1+2cos (pi / 2 - x) cos x

Answer 1

you know that sin^2 x + cos^2 x = 1, so when you expand you have

sin^2 x + 2 sinx cosx + cos^2 x

recall also that sec^2 x = 1 + tan^2 x

cos(pi/2-x) = sin(x)

So, what do you think?