已知:(x-y)²=20,xy=4,求X²+y²的值
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已知:(x-y)²=20,xy=4,求X²+y²的值
已知:(x-y)²=20,xy=4,求X²+y²的值
已知:(x-y)²=20,xy=4,求X²+y²的值
28
X²+y²
=(x-y)²+2xy
=20+4×2
=28
28
(x-y)^2=x^2-2xy+y^2
∴ 20=x^2+y^2-2(4)
x^2+y^2=28