x²/(x²-2)=3
x²=3x²-6
x²=3
原式=(1+x-1+x)/(1+x)(1-x)/[-x/(1-x²)+x]
=[2x/(1-x²)/[-x/(1-x²)+x]
上下同乘以1-x²
=2x/(-x+x-x³)
=2x/(-x³)
=-2/x²
=-2/3