
如果果一个点(x1,y1)旋转到(x2,y2),对应的角度旋转从θ1到θ1+θ2
sinθ1=y1/sqrt(x1*x1+ y1*y1)
cosθ1=x1/sqrt(x1*x1+ y1*y1)
cosθ1=x1/sqrt(x1*x1+ y1*y1)
sin(θ1+θ2)=sin(θ1)*cos(θ2)+cos(θ1)*sin(θ2)=y2/sqrt(x2*x2+y2*y2)
cos(θ1+θ2)=cos(θ1)*cos(θ2)-sin(θ1)*sin(θ2)=x2/sqrt(x2*x2+y2*y2)
根据上述推到出