已知x+y+=3,xy=2,求x²+y²和(x-y)²急用~.
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已知x+y+=3,xy=2,求x²+y²和(x-y)²急用~.
已知x+y+=3,xy=2,求x²+y²和(x-y)²
急用~.
已知x+y+=3,xy=2,求x²+y²和(x-y)²急用~.
x²+y²=x²+y²+2xy-2xy
=(x+y)²-2xy
=3^2-2*2=5
(x-y)²
=x²+y²+2xy-4xy
=(x+y)²-4xy
=3^2-4*2=1