Results 1 to 2 of 2

Math Help - differentiation...gah please help

  1. #1
    Newbie
    Joined
    Jul 2009
    Posts
    9

    Unhappy differentiation...gah please help

    hey this is an exam question i got stuck on,(im prob going to be posting a few of these just to let you know in advance lol) :

    differentiate (x^2 + 9) (4x^3 + 5) with respect to x,

    i know its where u have to use the dy over dx formula but i just have a hard time with this one and many others,so an easy explanation would be greatly appreciated as i am barely hanging on by a thread in ordinary level maths, the highest grade i have ever gotten is a C lol thanks!!

    the correct answer is :20x^4 + 108x^2 + 10x
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Super Member Matt Westwood's Avatar
    Joined
    Jul 2008
    From
    Reading, UK
    Posts
    802
    Thanks
    21
    Quote Originally Posted by cliste09 View Post
    hey this is an exam question i got stuck on,(im prob going to be posting a few of these just to let you know in advance lol) :

    differentiate (x^2 + 9) (4x^3 + 5) with respect to x,

    i know its where u have to use the dy over dx formula but i just have a hard time with this one and many others,so an easy explanation would be greatly appreciated as i am barely hanging on by a thread in ordinary level maths, the highest grade i have ever gotten is a C lol thanks!!

    the correct answer is :20x^4 + 108x^2 + 10x
    Do you know the product rule? The diff of one thing multiplied by another thing is equal to the one thing multiplied by the diff of the other added to the diff of the one thing multplied by the other:

    \frac d {dx} f(x)g(x) = g (x) \frac d {dx} f(x) + f(x) \frac d {dx} g(x)

    That should get you started. Now all you need to do is work out \frac d {dx} (x^2 + 9) and \frac d {dx} (4x^3 + 5).

    If you're not sure how to do that then another hint: "the power law" which you ought to make sure you've learned.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 2
    Last Post: July 26th 2010, 05:24 PM
  2. Differentiation and partial differentiation
    Posted in the Calculus Forum
    Replies: 2
    Last Post: May 30th 2010, 10:16 PM
  3. Differentiation
    Posted in the Calculus Forum
    Replies: 1
    Last Post: February 4th 2010, 10:45 AM
  4. Differentiation Help
    Posted in the Calculus Forum
    Replies: 1
    Last Post: January 25th 2010, 06:20 PM
  5. Differentiation and Implicit Differentiation
    Posted in the Calculus Forum
    Replies: 1
    Last Post: February 6th 2009, 04:07 AM

Search Tags


/mathhelpforum @mathhelpforum