1+h=1+h/2+h/2
1 =1+h/2-h/2
sin(1+h)=sin(1+h/2)*cos(h/2)+sin(h/2)*cos(1+h/2)
sin(1) =sin(1+h/2)*cos(h/2)-sin(h/2)*cos(1+h/2)
上面两式相减