Integration with trig identites

I got up to here, where do I go next? The question is on the very top.

I got up to here, where do I go next? The question is on the very top.

\cos^2 x -\sin^2 x \equiv \cos 2x

Have you ever integrated cos^2 before? There's a standard method to cos^2 and sin^2 (and tan^2 but it's a different identity).

I got up to here, where do I go next? The question is on the very top.

Your fourth line of working has the key to evaluating the integral.

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