trig identities

Pythagoean

1) sin² x+cos²x=1

2) 1+tan²x=sec²x

3) 1+cot²x=csc²x

Reciprocal

cot(x)= cos(x)/sin(x)

tan(X)=sin(x)/cos(X)

Double angle

sin2x=2 sin x cos x

cos 2x=cos²x-sin²x

cos2x=2 cos²x-1

cos2x=1-2sin²x