Math Is Fun Forum

baggins

Member

Registered: 2008-06-24

Posts: 5

derivative of the polynomial function

Hi Everyone,

Always making  small mistakes in my calculation but unfortunately that make me loose points:(

I would like to know if I didn't make any mistake on that question:

       This question concerns the function
                f(x)= x^3 +3x^2 − 9x+15.

      Find the stationary points of this function:

     The derivative of the polynomial function
         f(x) = x^3 + 3x^2 – 9x + 15

        f ’(x) = (3x^2) + 3(2x) – 9(1)
                = 3x^2 + 6x – 9
                = 3(x^2 + 2x – 3)
      The equation f ’(x) = 0 is equivalent to x^2+2x-3 = 0;
      That is, (x+3)(x-1) = 0
      Which give the stationary points:
      X= -3 and x= 1

Thanks for your help:)

luca-deltodesco

Member

Registered: 2006-05-05

Posts: 1,470

Re: derivative of the polynomial function

correct., although to find the stationary points, you should then substitue those two values of x to get 2 x,y pairs

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baggins

Member

Registered: 2008-06-24

Posts: 5

Re: derivative of the polynomial function

Thanks luca-deltodesco for your help:):D