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

5.3.1-Trigonometry-Simple-Identities-Diagram-2a  5.3.1-Trigonometry-Simple-Identities-Diagram-2b

How to use the identities


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.

Worked Example