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: Finding a function for the parabola

  1. Apr 28, 2010 #1
    Note: I don't need any answer, all I want to know is whether this question is possible.

    1. The problem statement, all variables and given/known data
    "What is the function of the parabola which has the points (1, 1) (2, 2) and (3, 3)?"
    I just asked my teacher to get the question, It's not stated in my text book.

    2. Relevant equations

    3. The attempt at a solution
    No idea! I don't get more than a linear function.

    - - - - -

  2. jcsd
  3. Apr 28, 2010 #2


    User Avatar
    Homework Helper

    While the points look linear, sub the points into y=ax2+bx+c. You'll get three equations with three unknowns.
  4. Apr 28, 2010 #3
    I did this and it turns out kinda ugly. I got 0 for the coefficient of the squared term (well, [tex]1.5x 10^{-14}[/tex] )I got 1 for the coefficient of the x term; and I got [tex]3x10^{-14}[/tex] for the constant. Looks pretty linear there...although not EXACTLY linear...but I may have made a mistake.

    EDIT: I started this by hand and it got ugly quick. I used my TI89 with the rref function and that's what it got. Those points are in a line...it's difficult to force the quadratic on it because they are so close together. One could plug those coefficients into the [tex]Ax^2+Bx+C=0[/tex]
    formula and complete the square...It's REALLY close to linear...and the thing could open up or down...those points are too close together and linear to really make sense of....as far as I can tell...
    Last edited: Apr 28, 2010
  5. Apr 28, 2010 #4
    At first it seemed very complicated, but when I uncovered the trick It was so easy.
    Yes, I know that it's not possible to write a second-degree equation for a linear graph, therefore I had to use 'limit' as a positive integer 'n' approaching 0.
    Thanks for the answers.
  6. Apr 29, 2010 #5


    User Avatar
    Science Advisor

    ??? An integer can't "approach" 0!
  7. Apr 29, 2010 #6
    Sorry, I just meant a positive rational number.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook