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化简并求值:已知x、y满足:x^2+y^2-4x+6y+13=0求代数式:(3x+y)^2-3(3x-y)(x+y)-(x-3y)(x+3y)的值麻烦了!帮帮我!...
化简并求值:
已知x、y满足:x^2+y^2-4x+6y+13=0
求代数式:(3x+y)^2-3(3x-y)(x+y)-(x-3y)(x+3y)的值
麻烦了!帮帮我! 展开
已知x、y满足:x^2+y^2-4x+6y+13=0
求代数式:(3x+y)^2-3(3x-y)(x+y)-(x-3y)(x+3y)的值
麻烦了!帮帮我! 展开
2个回答
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x^2+y^2-4x+6y+13=0
x²-4x+4+y²+6y+9=0
(x-2)²+(y+3)²=0
x-2=0,x=2
y+3=0,y=-3
把x=2.y=-3代入。则
(3x+y)²-3(3x-y)(x+y)-(x-3y)(x+3y)
=(9-3)²-3(9+3)(2-3)-(2+9)(2-9)
=9+27+77
=113
x²-4x+4+y²+6y+9=0
(x-2)²+(y+3)²=0
x-2=0,x=2
y+3=0,y=-3
把x=2.y=-3代入。则
(3x+y)²-3(3x-y)(x+y)-(x-3y)(x+3y)
=(9-3)²-3(9+3)(2-3)-(2+9)(2-9)
=9+27+77
=113
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