cos(a+b)=cos a * cos b - sin a * sin b

cos(a-b)=cos a * cos b + sin a * sin b

sin(a+b)=sin a * cos b + cos a * sin b

sin(a-b)=sin a * cos b - cos a * sin b

(2) Double angle formula

sin 2a = 2 sin a * cos a

cos 2a = 2 (cos a)^2 - 1

cos 2a = 1 - 2 (sin a )^2

Cos 2a = (cos a)^2-(symplectic a) 2

(3) General formula

Let tan a/2 = t

Sina = (1+t 2)/2t.

1+t^2)/( 1-t^2

Tan Yi = (1-t 2)/2t

(4) auxiliary angle formula

X sin a+y cos a = (x 2+y 2) * sin (a+b) under the radical sign, where tan b = y/x.

The above must be mastered.

There are also eight formulas of sum and difference multiplication, multiplication and difference, which do not need to be mastered. But if you master it, it will be much faster to solve the problem. Communicate with each other if necessary ~