若x+y=9,xy=20则 x^2+y^2=

网友回答

x²+y²
=(x+y)²-2xy
=81-40
=41(x-y)²
=x²+y²-2xy
=41-40
=1======以下答案可供参考======
供参考答案1:
x^2+y^2=__(x+y)^2-2xy=81-40=41___,
(x-y)^2=_x^2+y^2-2xy=41-40=1____
供参考答案2:
1、x²＋y²=(x＋y)²－2xy=41
2、(x－y)²=(x＋y)²－4xy=1