若x-y=2,x2-y2=10,则4x+6等于( )
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若x-y=2,x2-y2=10,则4x+6等于( )
A. 5
B. -5
C. -20
D. 20
A. 5
B. -5
C. -20
D. 20
![若x-y=2,x2-y2=10,则4x+6等于( )](/uploads/image/z/16967558-38-8.jpg?t=%E8%8B%A5x-y%3D2%EF%BC%8Cx2-y2%3D10%EF%BC%8C%E5%88%994x%2B6%E7%AD%89%E4%BA%8E%EF%BC%88%E3%80%80%E3%80%80%EF%BC%89)
由题意,得
x−y=2
x2−y2=10,即
x−y=2,①
(x+y)(x−y)=10,②
把①代入②,解得x+y=5,③
由①+③,得
2x=7,
则4x+6=2×2x+6=2×7+6=20.
故选D.
x−y=2
x2−y2=10,即
x−y=2,①
(x+y)(x−y)=10,②
把①代入②,解得x+y=5,③
由①+③,得
2x=7,
则4x+6=2×2x+6=2×7+6=20.
故选D.
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