x-y=9,xy=5,求x²+y²的值

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x-y=9,xy=5,求x²+y²的值
x-y=9,xy=5,求x²+y²的值

x-y=9,xy=5,求x²+y²的值
x²+y²
=(x²-2xy+y²)+2xy
=(x-y)²+2xy
=9²+2×5
=81+10
=91