设P(x,y)为函数y=x平方-1(x大于根号3)图象上一动点,记m=(x-1分之3x+y-5)+(y-2分之x+3y-

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  • 答:

    y=x^2-1

    m=(3x+y-5)/(x-1)+(x+3y-7)/(y-2)

    =(3x+x^2-1-5)/(x-1)+(x+3x^2-3-7)/(x^2-1-2)

    =(x^2+3x-6)/(x-1)+(3x^2+x-10)/(x^2-3)

    m'(x)=(2x+3)/(x-1)-(x^2+3x-6)/(x-1)^2+(6x+1)/(x^2-3)-(6x^3+2x^2-20x)/(x^2-3)^2

    =(x^2-2x+3)[1/(x-1)^2-1/(x^2-3)^2]

    =(x^2-2x+3)(x^2+x-4)(x^2-x-2)/[(x-1)^2*(x^2-3)^2]

    因为x>√3,因此只有x^2-x-2的值可能为0

    令m‘(x)=0,则:x^2-x-2=0,解得:x=2(x=-1不符合舍去)

    所以:

    当√3=0,m(x)是增函数.

    所以:当x=2时,m取得最小值为8

    把x=2代入抛物线方程y=x^2-1得y=3

    所以点P坐标为(2,3).