Trigonometry

Basic Identities
1) sin2θundefined+ cos2θ = 1

2) 1 + tan2θ = sec2θ

3) 1 + cot2θ = cosec2θ

Trigonometric Formulae for Compound Angles
sin(A+B) = sin AcosB + cosAsinB

sin(A-B) = sinAcosB - cosAsinB

For A + B = c, tanAtanBtanC = tanC - tanB - tanA

General Solution
If sinθ = 0    nπ

If cosθ = 0 (2n-1) π /2

If tanθ = 0 nπ

Sine Rule
a/sinA = b/sinB = c/sinC = k

Cosine Rule
a2 = b2+ c2 - 2bccosA

b2 = a2 + c2 - 2accasB

c2 = a2 + b2 - 2abcosC

Projection Rule
acosB + bcosA = 0

Inverse Trigonometric Ratios
(Principal value only)