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CALCULUS HELP?? the graph of the function f(x)=x^3+px^2+qx has a point of?

the graph of the function f(x)=x^3+px^2+qx has a point of inflection at (2,-22). determine exactly the constants p and q

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  • 9 years ago
    Favorite Answer

    f(x) = x³ + px² + qx

    The point (2,-22) is on the graph. This means that f(2) = -22.

    f(2) = 8 + 4p + 2q = -22 ==> 4p+2q = -30....(1)

    Since this is an inflection point, f '' (2) = 0.

    f ' (x) = 3x² + 2px

    f ''(x) = 6x + 2p

    f '' (2) = 12+2p = 0 ==> 2p = -12 ==> p = -6

    Plug p=-6 into (1):

    -24 + 2q = -30 ==> 2q =-6 ==> q = -3

  • 9 years ago

    derivative equations f(x) = x^3 + px^2 + qx

    f'(x) = 3x^2 +2px

    f''(x) = 6x + 2p

    when f''(x) = 0

    6x + 2p = 0

    <=> 6x = - 2p

    <=> x = - p/3

    I has a point of inflection at (2,-22) => x = -p/3 = 2

    => p = - 6

    Replace p =- 6 in f(x) = x^3 + px^2 + qx

    f(x) = x^3 - 6x^2 + qx (*)

    at this replace A (2 ; -22) in (*) with y = f(2) = -22

    -22 = 8 - 6.4 + 2q

    -22 = 2q - 16

    2q = -6

    => q = - 3

    So p = -6 , q = -3 the graph of the function f(x)=x^3+px^2+qx has a point of inflection at (2,-22)

  • 9 years ago

    x-axis value of inflection points are root of the 2nd derivative then:

    f ' ' (x) = 6x +2p = 0 then

    f ' ' (2) = 6*2+2p =0 then p = -6

    Now f(x) = x^3 - 6x^2 +qx and f(2) = -22

    8 - 24 +2q = 22

    q = 19

    f (x) = x^3 - 6x^2 + 19x

  • 5 years ago

    First change ( x=2, y= -22 ) to get the first eq 8 +4p +2q = - 22 ( eq a million) inflection aspect exhibits the 2d spinoff f ' ' ( x) = 6 x +2p = 0 and 0 = 12 + 2p ( eq 2 ) remedy equipment (a million) and (2) ==> ( p= -6 ,q = - 3 )

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