# AQA A Level Maths: Pure复习笔记5.3.1 Trigonometry - Simple Identities

### Trigonometry - Simple Identities

#### What is a trigonometric identity?

• Trigonometric identities are statements that are true for all values of x or theta (θ)
• They are used to help simplify trig equations before solving them
• The first two identities you must know are:

#### Where do these identities come from?

• Although you don’t need to know the proof for these identities it is important to understand where they come from

#### Exam Tip

• You’ll need to remember these identities as they aren’t in the formula booklet.
• If asked to show one thing is identical (≡) another look at what parts are missing –  for example, if tan x has gone it must have been substituted.