1）（x+y / x-y）+（2x / y-x）
=(x+y)/(x-y)-2x/(x-y)
=(x+y-2x)/(x-y)
=(y-x)/(x-y)
=-1
（2）（2x / x ² -y ² ）+（3x / y ² -x ² ）+【x / （x+y)(y-x）】
=2x/(x²-y²)-3x/(x²-y²)-x/(x²-y²)
=(2x-3x-x)/(x²-y²)
=-2x/(x²-y²)
（3）（x ² -x-2 / x+3）÷（2-x）+(x+1 / x+3）
=(x²-x-2)/(x+3)(2-x)+(x+1)/(x+3)
=(x²-x-2)/(x+3)(2-x)+(x+1)(2-x)/(x+3)(2-x)
=(x²-x-2+2x+2-x²-x)/(x+3)(2-x)
=0/(x+3)(2-x)
=0