已知sina+3cosa=2,则（sina-cosa)\(sina+cosa)=
问题描述：
已知sina+3cosa=2,则（sina-cosa)\(sina+cosa)=
答
sinA+3cosA=2 --->2sin(A/2)cos(A/2)+3[cos(A/2)^2-3(sin(A/2)]^2=2[cos(A/20]^2+[sin(A/2)]^2 --->4[sin(A/2)]^2+2sin(A/2)cos(A/)-2[cos(A/2)]^2=0【两边同除2[cos(A/2)]^2】 --->2[tan(A/2)]^2+tan(A/2)-1=0 --->...