tan(x)是不是写错了?假设tan(x)=2(1)原式上下同时除以cosx原式=(2+tanx)/(3tanx-1)=4/5(2)原式=(sinxcosx-1)/1=(sinxcosx-(sinx)^2-(cosx)^2)/((sinx)^2+(cosx)^2)上下同时除以(cosx)^2=(tanx-(tanx)^2-1)/((tanx)^2...