已知x+y=5,xy=-6,求3x^2+3y^2
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已知x+y=5,xy=-6,求3x^2+3y^2
![已知x+y=5,xy=-6,求3x^2+3y^2](/uploads/image/z/16593637-13-7.jpg?t=%E5%B7%B2%E7%9F%A5x%2By%3D5%2Cxy%3D-6%2C%E6%B1%823x%5E2%2B3y%5E2)
解3x^2+3y^2
=3(x^2+y^2)
=3(x^2+y^2+2xy-2xy)
=3[(x+y)^2-2xy]
=3[(5)^2-2×(-6)]
=3×(25+12)
=3×37
=111.
=3(x^2+y^2)
=3(x^2+y^2+2xy-2xy)
=3[(x+y)^2-2xy]
=3[(5)^2-2×(-6)]
=3×(25+12)
=3×37
=111.
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