已知x+y=4,xy=3,求下列各式的值.(x-y)² x²y=xy²

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已知x+y=4,xy=3,求下列各式的值.(x-y)² x²y=xy²

(x-y)²
=(x+y)²-4xy
=4²-4×3
=4
x²y-xy²
=xy(x-y)
=3*(±2)
=±6