1.已知x+1/x=4,则x²+1/x²的值是 ( )A.12 B.1/2 C.16 D.不能确定2.已知x=2009,y=2010,则(x+y)·x²+y²/x四次方-y四次方等于( )3.若x/3=y/4=z/7,则3x+y+z/y的值为( )
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![1.已知x+1/x=4,则x²+1/x²的值是 ( )A.12 B.1/2 C.16 D.不能确定2.已知x=2009,y=2010,则(x+y)·x²+y²/x四次方-y四次方等于( )3.若x/3=y/4=z/7,则3x+y+z/y的值为( )](/uploads/image/z/1166918-14-8.jpg?t=1.%E5%B7%B2%E7%9F%A5x%2B1%2Fx%3D4%2C%E5%88%99x%26sup2%3B%2B1%2Fx%26sup2%3B%E7%9A%84%E5%80%BC%E6%98%AF+%EF%BC%88+%EF%BC%89A.12+B.1%2F2+C.16+D.%E4%B8%8D%E8%83%BD%E7%A1%AE%E5%AE%9A2.%E5%B7%B2%E7%9F%A5x%3D2009%2Cy%3D2010%2C%E5%88%99%EF%BC%88x%2By%EF%BC%89%C2%B7x%26sup2%3B%2By%26sup2%3B%2Fx%E5%9B%9B%E6%AC%A1%E6%96%B9-y%E5%9B%9B%E6%AC%A1%E6%96%B9%E7%AD%89%E4%BA%8E%EF%BC%88+%EF%BC%893.%E8%8B%A5x%2F3%3Dy%2F4%3Dz%2F7%2C%E5%88%993x%2By%2Bz%2Fy%E7%9A%84%E5%80%BC%E4%B8%BA%EF%BC%88+%EF%BC%89)
1.已知x+1/x=4,则x²+1/x²的值是 ( )A.12 B.1/2 C.16 D.不能确定2.已知x=2009,y=2010,则(x+y)·x²+y²/x四次方-y四次方等于( )3.若x/3=y/4=z/7,则3x+y+z/y的值为( )
1.已知x+1/x=4,则x²+1/x²的值是 ( )
A.12 B.1/2 C.16 D.不能确定
2.已知x=2009,y=2010,则(x+y)·x²+y²/x四次方-y四次方等于( )
3.若x/3=y/4=z/7,则3x+y+z/y的值为( )
1.已知x+1/x=4,则x²+1/x²的值是 ( )A.12 B.1/2 C.16 D.不能确定2.已知x=2009,y=2010,则(x+y)·x²+y²/x四次方-y四次方等于( )3.若x/3=y/4=z/7,则3x+y+z/y的值为( )
1.(x + 1/x)^2 = x^2 + 2 + 1/x^2 = 16
所以答案是:14
2.原式=(x+y)(x^2 + y^2)/(x^2+y^2)(x^2-y^2) = 1/(x-y)=-1
3.由题可假设:x = 3t,y = 4t,z = 7t(满足条件)
代入= (3*3t + 4t + 7t)/(4t) = 5
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