Trigonometric Proof (Edexcel A Level Maths) : Revision Note
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Trigonometric Proof
Proving trigonometric identities
You can use trigonometric identities you already know to prove new identities
Make sure you know the simple trigonometric identities and further trigonometric identities
To prove an identity start on one side and proceed step by step until you get to the other side

Clever substitution into the compound angle formulae can be a useful tool for proving identities

Make sure you are confident handling fractions and fractions-within-fractions

Always keep an eye on the 'target' expression – this can help suggest what identities to use
Examiner Tips and Tricks
Don't forget that you can start a proof from either end – sometimes it might be easier to start from the right-hand side (see the Worked Example)
A number of trigonometric identities are given to you in the formulae booklet – make sure you know which ones are (and aren't) in there
Worked Example

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