Results 1 to 2 of 2

Math Help - Simple Graphing Question

  1. #1
    Newbie
    Joined
    Apr 2009
    Posts
    2

    Simple Graphing Question

    Ok, this is going to sound stupid... because I am majoring in math... and have been graphing simple graphs for years...... but I was just tutoring a kid.. and was trying to figure out a quadratic equation from looking at the graph.... and I have a complete brain fade.

    So.... if the equation is y = (1/4)x^2
    I thought.... you would make a table multiply by the reciprocal..

    *4 | x | y|
    -8 | -2|4
    -4| -1| 1
    0 |0 |0
    4 |1 |1
    8 | 2 |4
    12|3 |9

    but to do it the other way... clearly when x=2.. y = (1/4)x^2 = 2*2*0.25 = 1
    .... but in the way high school tells you to do horizontal stretch... why is it saying when x is 4, y is 1?
    What am I missing?
    Last edited by mr fantastic; December 8th 2009 at 12:55 PM. Reason: rt --> de
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor
    Grandad's Avatar
    Joined
    Dec 2008
    From
    South Coast of England
    Posts
    2,570
    Thanks
    1
    Hello gwalker11
    Quote Originally Posted by gwalker11 View Post
    Ok, this is going to sound stupid... because I am majoring in math... and have been graphing simple graphs for years...... but I was just tutoring a kid.. and was trying to figure out a quadratic equation from looking at the graph.... and I have a complete brain fade.

    So.... if the equation is y = (1/4)x^2
    I thought.... you would make a table multiply by the reciprocal..

    *4 | x | y|
    -8 | -2|4
    -4| -1| 1
    0 |0 |0
    4 |1 |1
    8 | 2 |4
    12|3 |9

    but to do it the other way... clearly when x=2.. y = (1/4)x^2 = 2*2*0.25 = 1
    .... but in the way high school tells you to do horizontal stretch... why is it saying when x is 4, y is 1?
    What am I missing?
    I'm not at all sure why you would want to multiply by the reciprocal. This is a method that I have never seen! But if you do it this way, you must first re-write the equation as:

    y=(\tfrac{1}{2}x)^2

    So you'll need to multiply by 2, not 4. Then start with multiples of 2:

    E.g.
    (-4)\text{ = value of }x \rightarrow (-2) \rightarrow 4 = \text{ value of }y

    (-2)\text{ = value of }x\rightarrow (-1)  \rightarrow 1 = \text{ value of }y

    ... and so on.

    Does that make sense?

    Grandad
    Last edited by mr fantastic; December 8th 2009 at 12:56 PM.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Help graphing using simple trig
    Posted in the Calculators Forum
    Replies: 11
    Last Post: July 29th 2011, 11:02 AM
  2. Replies: 1
    Last Post: May 22nd 2010, 12:44 AM
  3. Replies: 4
    Last Post: May 4th 2010, 10:08 AM
  4. simple graphing question relating to optics
    Posted in the Math Topics Forum
    Replies: 0
    Last Post: September 20th 2009, 12:59 PM
  5. Simple graphing problem giving me trouble
    Posted in the Trigonometry Forum
    Replies: 2
    Last Post: July 15th 2007, 01:16 PM

Search Tags


/mathhelpforum @mathhelpforum