Results 1 to 3 of 3
Like Tree2Thanks
  • 1 Post By richard1234
  • 1 Post By biffboy

Math Help - Differentiation help

  1. #1
    Junior Member
    Joined
    Mar 2009
    Posts
    34

    Differentiation help

    The gradient of a curve y= ax^2 +bx at the point (2,4) is -8, calculate the values of a and b
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Super Member
    Joined
    Jun 2012
    From
    AZ
    Posts
    616
    Thanks
    97

    Re: Differentiation help

    \frac{dy}{dx} = 2ax + b. Specifically, at (2,4), \frac{dy}{dx} = 2a(2) + b = 4a + b = -8.

    However...we have one equation, two variables. Can't really find a unique solution (a,b). However, we do know that, for the original equation, when x = 2, y = 4.

    4 = a(2^2) + b(2) = 4a + 2b, so we have the system


    4a + b = -8
    4a + 2b = 4

    Solve the system of equations.
    Thanks from kl050196
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Senior Member
    Joined
    Mar 2012
    From
    Sheffield England
    Posts
    440
    Thanks
    76

    Re: Differentiation help

    (2,4) is on curve so 4a+2b=4 Gradient=2ax+b When x=2 gradient=-8 so 4a+b=-8 Solve the simultaneous equations to find a and b
    Thanks from kl050196
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 2
    Last Post: July 26th 2010, 06:24 PM
  2. Differentiation and partial differentiation
    Posted in the Calculus Forum
    Replies: 2
    Last Post: May 30th 2010, 11:16 PM
  3. [SOLVED] Help with Differentiation
    Posted in the Calculus Forum
    Replies: 5
    Last Post: February 18th 2010, 05:05 AM
  4. Differentiation and Implicit Differentiation
    Posted in the Calculus Forum
    Replies: 1
    Last Post: February 6th 2009, 05:07 AM
  5. Differentiation
    Posted in the Calculus Forum
    Replies: 1
    Last Post: July 1st 2008, 04:25 AM

Search Tags


/mathhelpforum @mathhelpforum