已知sin(360°+α)-cos(180°-α)=m

问题描述:

已知sin(360°+α)-cos(180°-α)=m
则sin(180°+α)cos(180°-α)=?

sin(360°+α)-cos(180°-α)= sinα +cosα =m
(sinα +cosα)^2 = 1+2sinα*cosα =m^2,sinα*cosα=(m^2-1)/2
sin(180°+α)cos(180°-α)= -sinα(-cosα)=sinα*cosα=(m^2-1)/2