What is the answer to this question?

Choice A) 4, 3, 5, 1, 2

Explanation:

Since tan(x) = sin(x)/cos(x) is a known and widely used trig identity, this must mean step 4 goes first.

The answer is between choice A and choice B.

The question is now: What is the correct second step?

It's either step 3 (choice A) or step 5 (choice B)

It turns out that step 3 is the correct statement after step 4. The sin(2x) breaks up into 2sin(x)cos(x), while the cos(2x) breaks up into cos^2(x)-sin^2(x). There are three different variations for the cos(2x) and this just happens to be one of them.

So we can rule out choice B and go with choice A as the final answer.