1. Not finding help here? Sign up for a free 30min 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!

Finding the function

  1. Dec 14, 2007 #1
    1. The problem statement, all variables and given/known data
    Find a function f such that f'(x)=x^3 and the line x+y=0 is tangent to the graph of f.

    2. Relevant equations
    Need antiderivative

    3. The attempt at a solution
    I found the antiderivative, aka the function, to be (x^4)/4 + C
    Since the tangent like is x+y=0, --> y=-x, so the slope is -1
    If the slope is -1, that means the derivative, x^3 also equals -1
    Plugging in f(-1) gives 1/4 + C

    Now I don't know what to do with that.
  2. jcsd
  3. Dec 14, 2007 #2
    It is saying that the tangent to f is -1, not f itself.

  4. Dec 14, 2007 #3
    Well wouldn't it still be the same slope anyhow?
  5. Dec 15, 2007 #4


    User Avatar
    Staff Emeritus
    Science Advisor

    Where (what x) is the slope of x4/4+ C equal to -1? If x+ y= 0 is tangent to y= x4/4+ C they must have the same y value there.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: Finding the function
  1. Finding a function (Replies: 13)

  2. Find these function! (Replies: 1)