已知x+y=8,xy=12,求x²+y²的值

已知x+y=8,xy=12,求x²+y²的值
已知x+y=8,xy=12,求x²+y²的值

已知x+y=8,xy=12,求x²+y²的值
x²+y²
=(x+y)²-2xy
=8x8-2x12
=64-24
=40
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x²+y²
=x²+2xy+y²-2xy
=（x+y）²-2xy
=64-24
=40

x²+y²=(x+y)²-2xy=64-24=40;