1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Curve Sketching: Solving for b and d: f(x)=x^3+bx^2+d

  1. Jun 11, 2012 #1
    1. The problem statement, all variables and given/known data

    f(x)=x^3+bx^2+d given a critical point of (2,-4), solve for b and d

    2. Relevant equations

    f'(x)=3x^2+2bx ?

    3. The attempt at a solution

    I wasn't really sure where to go with this.

    So I know that a critical point happens when f'(x)=0, and this point can be either a max, min, or extrema.

    I tried making the derivative = to 0 and then subbed in the x value from the critical point of x=2. But i believe that this is definitely not right.

    Any help is much appreciated, thank you.
     
  2. jcsd
  3. Jun 11, 2012 #2

    Mark44

    Staff: Mentor

    From the given information, you know that f(2) = 4 and f'(2) = 0. This will give you two equations in your two unknowns so that you can solve for b and d.
     
  4. Jun 11, 2012 #3

    HallsofIvy

    User Avatar
    Staff Emeritus
    Science Advisor

    No, that definitely is right! So what did you get when you put x= 2 into f'(x)= 0?
     
  5. Jun 11, 2012 #4
    Oh yeeesss! Thank you! I knew i would have to get two unknowns from somewhere then solve!
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Curve Sketching: Solving for b and d: f(x)=x^3+bx^2+d
  1. Sketch f(x)=x^3-2x^2+5 (Replies: 3)

Loading...