Results 1 to 5 of 5

Math Help - Another derivative problem

  1. #1
    Member
    Joined
    Oct 2011
    Posts
    86
    Thanks
    2

    Another derivative problem

    I'm just getting into derviatives as a rate of change.

    The equation of a moving body is given by 3t^2 - 5t + 7 feet.

    My book says that the velocity is the derivative of this equation and that is 6t-5

    However I got something completely different when I derived the first equation.

    Then the derivative of 6t-5 at t=3 ends up being 6. But I still don't get that.

    What am I doing wrong?
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor
    skeeter's Avatar
    Joined
    Jun 2008
    From
    North Texas
    Posts
    11,621
    Thanks
    426

    Re: Another derivative problem

    Quote Originally Posted by Nervous View Post
    I'm just getting into derviatives as a rate of change.

    The equation of a moving body is given by 3t^2 - 5t + 7 feet.

    My book says that the velocity is the derivative of this equation and that is 6t-5

    However I got something completely different when I derived the first equation.

    Then the derivative of 6t-5 at t=3 ends up being 6. But I still don't get that.

    What am I doing wrong?
    position ...

    x(t) = 3t^2 - 5t + 7

    velocity is the derivative of position ...

    x'(t) = v(t) = 6t - 5

    v(3) = 6(3) - 5 = 13
    Follow Math Help Forum on Facebook and Google+

  3. #3
    MHF Contributor

    Joined
    Apr 2005
    Posts
    15,303
    Thanks
    1278

    Re: Another derivative problem

    Quote Originally Posted by Nervous View Post
    I'm just getting into derviatives as a rate of change.

    The equation of a moving body is given by 3t^2 - 5t + 7 feet.

    My book says that the velocity is the derivative of this equation and that is 6t-5

    However I got something completely different when I derived the first equation.

    Then the derivative of 6t-5 at t=3 ends up being 6. But I still don't get that.

    What am I doing wrong?
    Do you understand that we can't tell you what you did wrong when you haven't told us what you did?
    What did you do and what result did you get?

    (Do you know the standard formula for the derivative of x^n?)
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Member
    Joined
    Oct 2011
    Posts
    86
    Thanks
    2

    Re: Another derivative problem

    I figured it out...
    I knew that both (3)' and (5)' equaled 0, but I didn't multiply zero by their neighbors when I applied the product rule.
    Follow Math Help Forum on Facebook and Google+

  5. #5
    MHF Contributor
    skeeter's Avatar
    Joined
    Jun 2008
    From
    North Texas
    Posts
    11,621
    Thanks
    426

    Re: Another derivative problem

    Quote Originally Posted by Nervous View Post
    I figured it out...
    I knew that both (3)' and (5)' equaled 0, but I didn't multiply zero by their neighbors when I applied the product rule.
    huh ???
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. derivative problem
    Posted in the Calculus Forum
    Replies: 4
    Last Post: September 25th 2010, 08:33 PM
  2. derivative problem
    Posted in the Calculus Forum
    Replies: 0
    Last Post: March 2nd 2010, 03:21 PM
  3. derivative problem
    Posted in the Calculus Forum
    Replies: 3
    Last Post: September 18th 2009, 01:56 PM
  4. A derivative problem?
    Posted in the Calculus Forum
    Replies: 6
    Last Post: October 10th 2008, 06:29 PM
  5. derivative problem help
    Posted in the Calculus Forum
    Replies: 2
    Last Post: April 6th 2008, 06:48 AM

Search Tags


/mathhelpforum @mathhelpforum