What are the most important trig identities we need to know?

cos^2(A) + sin^2(A) = 1, sin(A+B) = sinAcosB + cosAsinB, cos(A+B) = cosAcosB - sinAsinB, sin2A = 2sinAcosA (if A = B), cos2A = cos^2(A) - sin^2(A) (if A = B), cos2A = 1 - 2sin^2(A) => sin^2(A) = 1/2(1 - cos2A), cos2A = 2cos^2(A) - 1 => cos^2(A) = 1/2(1 + cos2A), learn these as must be used to integrate powers of trig functions.