Sum and difference identities  Trigonometric Identities
Sum and difference identities
Trig identities are formulas developed based on Pythagorean Theorem. These identities show us how and where to find the sine, cosine, and tangent of the sum and difference of two given angles.
Basic concepts:
 Use sine ratio to calculate angles and side (Sin = $\frac{o}{h}$ )
 Use cosine ratio to calculate angles and side (Cos = $\frac{a}{h}$ )
 Use tangent ratio to calculate angles and side (Tan = $\frac{o}{a}$ )
 Trigonometric ratios of angles in radians
Related concepts:
 Solving trigonometric equations using sum and difference identities
Lessons
Notes:
Download the Trigonometry identities chart here
Formulas:$\sin (A + B)$
$\sin (A  B)$
$\cos (A + B)$
$\cos (A  B)$
$\tan (A + B)$
$\tan (A  B)$

1.
Simplify expressions

2.
Prove Identities

3.
Without using a calculator, evaluate: