# AQA A Level Maths: Pure复习笔记5.8.1 Trigonometric Proof

### 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

#### Exam Tip

• 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