2x/(5x-3)除3/（25x²-9）乘x/(5x+3）=2x/(5x-3)×(5x+3)(5x-3)/3×x/(5x+3)=2x²/3通分x-y/(2x+2y)与xy/(x+y)²(x-y)/(2x+2y)=(x-y)(x+y)/2(x+y)²xy/(x+y)²=2xy/2(x+y)²