Results 1 to 3 of 3

Math Help - random calculus questions

  1. #1
    Junior Member
    Joined
    Mar 2009
    Posts
    32

    random calculus questions



    i worked it out by differentiating f(y) and then g(y) to get:

    5Ay^-6 + Be^y

    but that's not hte right answer. am i differentiating wrong?

    Find the equations of the tangent line, y1, and the normal line, y2 to the following curve at the given point P.




    for y1 i got the derivative of y to get 4x^3 + 9e^x
    and for y2 it should be the same thing since x is 0, i'm not sure what i'm doing wrong since both my answers are incorrect

    Find a second-degree polynomial P such that the following conditions are met. P (6) = 8
    P ' (6) = 8
    P '' (6) = 4

    this one is puzzling me as i'm not sure whre to start, should i start w/ functions that will work for original or should i start at the p"? not sure
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Grand Panjandrum
    Joined
    Nov 2005
    From
    someplace
    Posts
    14,972
    Thanks
    4
    Quote Originally Posted by deltemis View Post


    i worked it out by differentiating f(y) and then g(y) to get:

    5Ay^-6 + Be^y

    but that's not hte right answer. am i differentiating wrong?
    It would help if you say what you are supposed to do, but lets assume you are asked to differentiate z, but with respect to what? I will assume y, so:

    \frac{dz}{dy}=\frac{d}{dy}\left[\frac{A}{y^5}\right]+\frac{d}{dy}\left[Be^y\right] = -\, \frac{5A}{y^6}+Be^y

    CB
    Follow Math Help Forum on Facebook and Google+

  3. #3
    MHF Contributor

    Joined
    Apr 2005
    Posts
    15,373
    Thanks
    1314
    Quote Originally Posted by deltemis View Post


    i worked it out by differentiating f(y) and then g(y) to get:

    5Ay^-6 + Be^y

    but that's not hte right answer. am i differentiating wrong?
    I presume that you wrote f(y) as Ay^{-5}+ Be^y and then used the fact that the derivative of y^n is ny^{n-1} and the derivative of e^y is e^yj. That would give - 5Ay^{-6}+ Be^y. Do you see the difference?

    Find the equations of the tangent line, y1, and the normal line, y2 to the following curve at the given point P.




    for y1 i got the derivative of y to get 4x^3 + 9e^x
    and for y2 it should be the same thing since x is 0, i'm not sure what i'm doing wrong since both my answers are incorrect
    Yes, that is the correct derivative but what did you then do to find the tangent line? The tangent line at (0, 9) has slope 4(0^3)+ 9(e^0)= 9 and the normal line will have slope -1/9.

    Find a second-degree polynomial P such that the following conditions are met. P (6) = 8
    P ' (6) = 8
    P '' (6) = 4

    this one is puzzling me as i'm not sure whre to start, should i start w/ functions that will work for original or should i start at the p"? not sure
    Start by writing your polynomial as P(x)= Ax^2+ Bx+ C, a general second degree polynomial. Find P' and P" from that. Setting P(6)= 8, P'(6)= 8, and P''(6)= 4 will give you three equations for A, B, and C.

    It might be even easier if you write the polynomial as P(x)= A(x- 6)^2+ B(x- 6)+ C which is also a perfectly good "general second degree polynomial".
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Random Calculus Question
    Posted in the Calculus Forum
    Replies: 2
    Last Post: April 24th 2009, 11:46 PM
  2. Three Random Questions....
    Posted in the Calculus Forum
    Replies: 3
    Last Post: December 4th 2008, 05:09 PM
  3. a few random questions.
    Posted in the Algebra Forum
    Replies: 3
    Last Post: July 31st 2008, 09:07 AM
  4. Some Random Questions....
    Posted in the Math Topics Forum
    Replies: 4
    Last Post: October 28th 2006, 11:21 AM

Search Tags


/mathhelpforum @mathhelpforum