What is a trigonometric identity?

• They are used to help simplify trigonometric equations before solving them
• Sometimes you may see identities written with the symbol?≡
  • This means 'identical to'

What trigonometric identities do I need to know?

• The two trigonometric identities you must know are

Where do the trigonometric identities come from?

• You do not need to know the proof for these identities but it is a good idea to know where they come from
• From SOHCAHTOA we know that
• • This is not included in the formula booklet but is useful to remember

How are the trigonometric identities used?

• Most commonly trigonometric identities are used to change an equation into a form that allows it to be solved
• They can also be used to prove further identities such as the?double angle formulae