设t=tanx
t^2+2t-3=0
(t+3)(t-1)=0
t=-3或t=1
∵x∈第二象限
∴t=-3
(2sinx-cosx)/(sinx+2cosx) [上下同时除于cosx]
=(2tanx-1)/(tanx+2)
=[2*(-3)-1]/(-3+2)
=(-7)/(-1)
=7