已知x2+y2 =7,xy=-2.求5x2 -3xy-4y2 -11xy-7x2 +2y2

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已知x2+y2=7,xy=-2.求5x2-3xy-4y2-11xy-7x2+2y2已知x2+y2=7,xy=-2.求5x2-3xy-4y2-11xy-7x2+2y2已知x2+y2=7,xy=-2.求5

已知x2+y2 =7,xy=-2.求5x2 -3xy-4y2 -11xy-7x2 +2y2
已知x2+y2 =7,xy=-2.求5x2 -3xy-4y2 -11xy-7x2 +2y2

已知x2+y2 =7,xy=-2.求5x2 -3xy-4y2 -11xy-7x2 +2y2
x+y=7 xy=2
7^2=(x+y)^2=x^2+2xy+y^2=x^2+y^2+2*2
x^2+y^2=45
(1)y=7-x x(7-x)=2
x^2-7x+2=0
x=(7+41^(1/2))/2或x=(7-41^(1/2))/2
2x^2=(90+14*41^(1/2))/2,或=(90-14*41^(1/2))/2
(2) (x-y)^2=x^2-2xy+y^2=45-2*2=41

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