1-x/(1+x+x²)+6/(1-x)=7/(1-x)
1-x/(1+x+x²)=1/(1-x)
两边同时乘以(1-x)(1+x+x²)
1-x³-x(1-x)=1+x+x²
x³+2x=0
x(x²+2)=0
x=0