已知xy=4满足想x²y-xy²-x+y=56.求x²+y²的值
问题描述:
已知xy=4满足想x²y-xy²-x+y=56.求x²+y²的值
答
x²y-xy²-x+y
=xy(x-y)-(x-y)
=(xy-1)(x-y)
=56 xy=4
x-y=56/3
x²+y²=(x-y)^2+2xy=56^2/9+8