Results 1 to 4 of 4

Math Help - derivative

  1. #1
    Member maybeline9216's Avatar
    Joined
    Sep 2008
    From
    Singapore~
    Posts
    108

    Red face derivative

    Please help me with the circled qns (ii) and qn (a) and (b)

    see if you can get the paper's answer: (ii): -0.962
    qn (a) -13/9 < k<3
    (b) a=1,b=-10

    if u can pls tell me yr workings
    Attached Thumbnails Attached Thumbnails derivative-inidhelp.jpg  
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor
    Joined
    Aug 2007
    From
    USA
    Posts
    3,111
    Thanks
    2
    II

    I agree with the Paper's answer. It seems to me that it would be very difficult to get the integral wrong if you managed to partial frations correctly. What did you get for the partial fraction decomposition?

    2 - x + what/(x+5) - what/(x-5)

    a

    Get everything on the left side and look at it. Gather like terms until it looks like a quadratic. What happens when the discriminant is less than zero?

    b

    You have x = 2.

    From the line, you can determine the coordinates of the point of tangency. Substitute x = 2 and y = ????? into the cubic.

    From the slope of the line, you can determine the value of the first derivative of the cubic. Substitute x = 2 into the derivative and y`(2) = the slope of the line.

    You may have a little algebra after that.

    Those are the workings.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Member maybeline9216's Avatar
    Joined
    Sep 2008
    From
    Singapore~
    Posts
    108
    (ii) i got the correct answer for the partial fraction as stated in the paper...but when i integrate it i got a different answer..
    i got -x +2 + 3/10(1/5+x) + 3/10(1/5-x) as the partial fraction

    and when u integrate 3/10(1/5+x) dx, is it equal to 3/10[1n(5+x)]4,1 ?? P.S 4,1 is supposed to be beside top n bottom of the [] bracket

    (a) why is it dat the discriminant is less than zero?

    (b)From the slope of the line, you can determine the value of the first derivative of the cubic. wat do u mean by this? wad is the first derivative?
    Last edited by maybeline9216; September 1st 2008 at 07:09 AM. Reason: i forgot to write something
    Follow Math Help Forum on Facebook and Google+

  4. #4
    MHF Contributor
    Joined
    Aug 2007
    From
    USA
    Posts
    3,111
    Thanks
    2
    i got -x +2 + 3/10(1/5+x) + 3/10(1/5-x) as the partial fraction
    Get a little better at the notation. It's okay for now, because I already know what you mean. "3/10(1/5+x)" this is bad. You mean (3/10)*(1/(5+x)) - a couple extra parentheses clear it up.

    and when u integrate 3/10(1/5+x) dx, is it equal to 3/10[1n(5+x)]4,1 ?? P.S 4,1 is supposed to be beside top n bottom of the [] bracket
    Okay, but I must wonder if you got the last one. [int 1/(5-x) dx] is NOT ln(5-x) + C. You tell me what is wrong with it.

    (a) why is it dat the discriminant is less than zero?
    What do you remember about quadratic equations? It means, "No Real Solutions". Why is that helpful?

    (b)From the slope of the line, you can determine the value of the first derivative of the cubic. wat do u mean by this? wad is the first derivative?
    Now we have a problem. If you have integral problems, you should already be familiar with derivative problems.

    f(x) = ax^3 + b*x

    f`(x) = 3ax^2 + b

    Ringing any bells?
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. contuous weak derivative $\Rightarrow$ classic derivative ?
    Posted in the Differential Geometry Forum
    Replies: 2
    Last Post: April 22nd 2011, 03:37 AM
  2. Replies: 0
    Last Post: January 24th 2011, 12:40 PM
  3. [SOLVED] Definition of Derivative/Alt. form of the derivative
    Posted in the Calculus Forum
    Replies: 2
    Last Post: September 23rd 2010, 07:33 AM
  4. Derivative Increasing ==> Derivative Continuous
    Posted in the Differential Geometry Forum
    Replies: 2
    Last Post: February 23rd 2010, 11:58 AM
  5. Replies: 2
    Last Post: November 6th 2009, 03:51 PM

Search Tags


/mathhelpforum @mathhelpforum