解法一：设k∈{1,2,3},令θ=kπ/7,tan3θ+tan4θ=0(tanθ+tan2θ)/(1-tanθtan2θ)+2tan2θ/[1-(tan2θ)^2]=0tanθ+3tan2θ-3tanθ*(tan2θ)^2-(tan2θ)^3=0令tanθ=x,x+6x/(1-x^2)-12*x^3/(1-x^2)^2-8*x^3/(1-x^2)^...