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!

Inverse function help

  1. May 6, 2008 #1
    Ok, I decided to review basic algebra since I haven't done anything with it in like, forever. I came across an inverse function problem that I can't get the right answer.

    the equation is:

    y = cuberoot(x+sqrt(1+x^2)) + cuberoot(x-sqrt(1+x^2))

    I tried replacing X with Y, and solving for Y
    and getting rid of the cube roots by cubing both sides
    X^3 = y + sqrt(1+y^2) + y - sqrt(1+y^2)
    simplifying a bit (the square roots go away)
    x^3 = 2y
    so
    y = (1/2)x^3

    Yet the book I'm using says the answer is y=(1/2)(3x+x^3)

    What did I do wrong?
     
  2. jcsd
  3. May 6, 2008 #2

    Shooting Star

    User Avatar
    Homework Helper

    (a+b)³ =/= a³ + b³, as you have done.

    Use (a+b)³ = a³ + b³ +3ab(a+b).

    Start with y = a+b, and cube both sides. If you put a+b=y again, the result comes quickly,
     
  4. May 6, 2008 #3
    thanks, I think I got it. Man, a few years ago I could have done this, but now? I feel like a 9th grader again.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Inverse function help
  1. Inverse function help (Replies: 2)

Loading...