已知x-2y=15,xy=-25,求 x²+4y²-1的值?

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已知x-2y=15,xy=-25,求 x²+4y²-1的值?
已知x-2y=15,xy=-25,求 x²+4y²-1的值?

已知x-2y=15,xy=-25,求 x²+4y²-1的值?
x²+4y²-1
=(x-2y)²+4xy-1
把x-2y=15,xy=-25代入上式,得
x²+4y²-1
=(x-2y)²+4xy-1
=15²+4×(-25)-1
=225-100-1
=125-1
=124

324

已知x-2y=15，xy=-25
那么x²+4y²-1=(x-2y)²+4xy-1=15²+4*(-25)-1=124

x²+4y²-1=x²-4xy+(2y)²+4xy-1=(x-2y)²+4xy-1=15²+4(-25)-1=124

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