1/(1-9x^2)-(3x+1)/(3x-1)=(1-3x)/(1+3x)
1/(1+3x)(1-3x)+(3x+1)/(1-3x)=(1-3x)/(1+3x)
两边乘以(1+3x)(1-3x),得
1+(1+3x)^2=(1-3x)^2
1+1+6x+9x^2=1-6x+9x^2
6x+2=1-6x
12x=-1
x=-1/12