## Trig Identities (important)

*cos²x + sin²x= 1*

*tan²x = sec²x - 1*

*cot²x = cosec²x - 1*

## Double angle (important)

*sin2x = 2sinxcosx*

*cos2x = cos²x - sin²x*

* = 2cos²x - 1 **

* = 1 - 2sin²x **

*These can be made by rearranging cos²x + sin²x= 1 and subbing it into the equation.

## R

*R cos (θ ± α) = R cos θ cos α ∓ R sin θ sin α*

*R sin (θ ± α) = R sin θ cos α ± R cos θ sin α*

**Instructions**

○ Pick the correct formula

○ Compare to equation

○ Put Rcos and Rsin equal to their numbers

○ Square those numbers to find R squared then sqrt

○ Use sin/cos to find tan α

○ Put back into form - shorter equation with one trig identity.

## Addition Formulae

*sin(A ± B) = sinAcosB ± cosAsinB*

*cos(A ± B) = cosAcosB ∓ sinAsinB*

*tan(A ± B) = tanA ± tanB / 1 ∓ tanAtanB*

## Half angle formulae

Used to find an equation with two of the same trig identities but with different X values

e.g. to find in form **sin A + sin B**

Given on the formula sheet

Sec

cosec

Cot

Arcsin

Arccos

Arctan