1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Implicit Differentiation - Second Derivative

  1. Apr 1, 2006 #1
    Were assigned questions regarding implicit differentiation and the second derivative but did not receive a formal lesson so I need some explanations.


    Find the second derivative
    x^3 + y^3 = 1

    I found this solution on the internet and the answer matches the one in the textbook.

    http://img95.imageshack.us/img95/1240/implic44fz.gif [Broken]

    However, I don't understand how -2xy^3 - 2x^4/y^5 turned into just -2xy^3/y^5 (This is the 5-6 step). Furthermore, I don't see how -2xy^3/y^5 equals -2x(y^3 + x^3)/y^5 (6-7 step).

    Simply, I need explanations for this solutions rationale. Thanks.
    Last edited by a moderator: May 2, 2017
  2. jcsd
  3. Apr 1, 2006 #2


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    There is an obvious typo in step 5-6...the -2x^4/y^5 term disappears and then reappears on the next line .

    At the very end they use x^3+y^3=1, which was the initial equation.
    Last edited by a moderator: May 2, 2017
  4. Apr 1, 2006 #3
    Ahhh, now I see it, thanks for pointing that out!
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook