cos+cos=? 就是高中学的那四个公式

cosa+cosb=2cos[(a+b)/2]*cos[(a-b)/2]
cosa-cosb=-2sin[(a+b)/2]*sin[(a-b)/2]
sina+sinb=2sin[(a+b)/2]*cos[(a-b)/2]
sina-sinb=2cos[(a+b)/2]*sins[(a-b)/2]

sin(a)+sin(b)=2sin((a+b)/2)cos((a-b)/2)
sin(a)-sin(b)=2cos((a+b)/2)cos((a-b)/2)
cos(a)+cos(b)=2cos((a+b)/2)cos((a-b)/2)
cos(a)-cos(b)=-2sin((a+b)/2)sin((a-b)/2)

sin(α+β)+sin(α-β)=2sinαcosβ.
sin(α+β)-sin(α-β)=2cosαsinβ.
cos(α+β)+cos(α-β)=2cosαcosβ,
cos(α+β)- cos( α-β)=-2sinαsinβ.

cosx+cosy=2[cos(x+y)/2 * cos(x-y)/2]
cosx-cosy=-2[sin(x+y)/2 * sin(x-y)/2]
sinx+siny=2[sin(x+y)/2 * cos(x-y)/2]
sinx-siny=2[cos(x+y)/2 * sin(x-y)/2]
另外四个是：
sinx*cosy=1/2[sin(x+y)+sin(x-y)]
cosx*siny=1/2[sin(x+y)-sin(x-y)]
cosx*cosy=1/2[cos(x+y)+cos(x-y)]
sinx*siny=-1/2[cos(x+y)-cos(x-y)]

SIN(X+Y)=SINXCOSY+COSXSANY
COS(X+Y)=COSXCOSY-SINXSINY

我也忘了。。