已知x+y=7 xy=2 求2x²+2y²的值
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已知x+y=7 xy=2 求2x²+2y²的值
![已知x+y=7 xy=2 求2x²+2y²的值](/uploads/image/z/15672053-29-3.jpg?t=%E5%B7%B2%E7%9F%A5x%2By%3D7+xy%3D2+%E6%B1%822x%26%23178%3B%2B2y%26%23178%3B%E7%9A%84%E5%80%BC)
2x²+2y²
=2(x²+y²)
=2[(x²+2xy+y²)-2xy]
=2[(x+y)²-2xy]
=2(x+y)²-4xy
=2×7²-4×2
=98-8
=90
请点击下面的【选为满意回答】按钮.
=2(x²+y²)
=2[(x²+2xy+y²)-2xy]
=2[(x+y)²-2xy]
=2(x+y)²-4xy
=2×7²-4×2
=98-8
=90
请点击下面的【选为满意回答】按钮.
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