答：tanx=-3/42+sinxcosx-(cosx)^2=2(sinx)^2+2(cosx)^2+sinxcosx-(cosx)^2=[ 2(sinx)^2+(cosx)^2+sinxcosx ] / [ (sinx)^2+(cosx)^2 ] 分子分母同时除以(cosx)^2=[ 2(tanx)^2+1+tanx ] / [ (tanx)^2+1]=[ 2*(-3/4)^...