Here's an outline - you can fill in the details.

You have .

Substitute and do a bit of simplifying.

You end up with .

This factorises: .

Therefore .

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There are two things you should never try to prove: the impossible and the obvious.

The greater danger for most of us lies not in setting our aim too high and falling short; but in setting our aim too low and achieving our mark. (Michelangelo Buonarroti)

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