已知x+y=9,xy=4,则x^2+y^2=____,(x-y)^2=___
问题描述:
已知x+y=9,xy=4,则x^2+y^2=____,(x-y)^2=___
答
(x+y)²=81
x²+y²+2xy=81
x²+y²=81-2xy=73
(x-y)²=(x+y)²-4xy=81-16=65