先化简,再求值:(x²)/(x²-2xy+y²)÷(x²+2xy+y²)/(x²-y²),其中x=3

问题描述:

先化简,再求值:(x&sup2)/(x&sup2-2xy+y&sup2)÷(x&sup2+2xy+y&sup2)/(x&sup2-y&sup2),其中x=3
y=4

(x²)/(x²-2xy+y²)÷(x²+2xy+y²)/(x²-y²)
=(x²)/(x-y)²÷(x+y)²/(x+y)(x-y)
=x² / (x-y)² * (x+y)(x-y) / (x+y)²
=x² / (x-y)(x+y)
=x² / (x²-y²)
把x=3,y=4代入
原式=3² / (3²-4²)
=-9/7