和差化积公式
sin(a)+sin(b)=2sin(a+b2)cos(a-b2)
sin(a)−sin(b)=2cos[(a+b)/2]sin[(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]
4.积化和差公式
sin(a)sin(b)=-1/2[cos(a+b)-cos(a-b)]
cos(a)cos(b)=1/2[cos(a+b)+cos(a-b)]
sin(a)cos(b)=1/2[sin(a+b)+sin(a-b)]