Question

sin(x+T)-sinx=-T怎么变成2sinT/2*cos(x+T/2)=-T

Answer 1

sin(x+T)-sinx=sin(x+T/2+T/2)-sin(x+T/2-T/2)

=sin(x+T/2)*cosT/2+cos(x+T/2)*sinT/2-[sin(x+T/2)*cosT/2-cos(x+T/2)*sinT/2]

=2sinT/2*cos(x+T/2)

所以2sinT/2*cos(x+T/2)=sin(x+T)-sinx=-T