20.2 Sum and difference 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:
 Using sine ratio to calculate angles and side (Sin = $\frac{o}{h})$
 Using cosine ratio to calculate angles and side (Cos = $\frac{a}{h}$)
 Using tangent ratio to calculate angles and side (Tan = $\frac{o}{a} )$
 Trigonometric ratios for 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: