Can Trig Identities Be Proven Using Basic Trigonometric Functions?

[ttpp1124]

Homework Statement

I believed I've proved it right, but can someone confirm?

Relevant Equations

n/a

 

[member 587159]

I believe it is correct, but note that

$$(\tan^2 x -1)/\sec^2 x = (\tan^2 x -1) \cos^2 x = \sin^2 x - \cos^2 x = - \cos(2x)$$

so you could have been a little faster.