Results 1 to 9 of 9

Math Help - quadratic functions

  1. #1
    Junior Member
    Joined
    Sep 2009
    Posts
    66

    quadratic functions

    Find expressions for the quadratic functions whose graphs are shown.
    f(x) =
    g(x) =

    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor
    Joined
    Oct 2005
    From
    Earth
    Posts
    1,599
    The normal form we work with discussing parabolas is y=ax^2+bx+c. You need to find what "a" and "c" are. You have two variables and two points to work with. That's enough to solve for each variable.

    Make sense?

    EDIT: Big mistake, my apologies. See below post to clarify.
    Last edited by Jameson; September 9th 2009 at 05:01 PM.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Junior Member
    Joined
    Sep 2009
    Posts
    66
    that works for g(x) but not f(x) becuase there is only one point (the 3,0 doesnt seem to work)
    Follow Math Help Forum on Facebook and Google+

  4. #4
    MHF Contributor
    Joined
    Oct 2005
    From
    Earth
    Posts
    1,599
    Quote Originally Posted by kyleu03 View Post
    that works for g(x) but not f(x) becuase there is only one point (the 3,0 doesnt seem to work)
    You have another point, (4,2). See?
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Junior Member
    Joined
    Sep 2009
    Posts
    66
    Quote Originally Posted by Jameson View Post
    You have another point, (4,2). See?
    what forumla would i use? the point-slope?
    Follow Math Help Forum on Facebook and Google+

  6. #6
    MHF Contributor
    Joined
    Oct 2005
    From
    Earth
    Posts
    1,599
    Quote Originally Posted by kyleu03 View Post
    what forumla would i use? the point-slope?
    I made a big mistake, my apologies. The normal form should be y=ax^2+bx+c. There are three variables to solve for, a b and c. So you need three pairs of (x,y) points to be able to solve for a b and c. G(x) gives you three points but for F(x) you have to use the fact that the parabola is symmetrical to get a third point.

    Since you have the point (4,2) you can deduce that there is also the point (2,2) on the graph. Now you plug in your three (x,y) pairs into the equation I wrote above and solve for your a, b and c.
    Last edited by Jameson; September 9th 2009 at 06:07 PM.
    Follow Math Help Forum on Facebook and Google+

  7. #7
    Super Member 11rdc11's Avatar
    Joined
    Jul 2007
    From
    New Orleans
    Posts
    894
    Quote Originally Posted by Jameson View Post
    I made a big mistake, my apologies. The normal form should be y=ax^2+bx+c. There are three variables to solve for, a b and c. So you need three pairs of (x,y) points to be able to solve for a b and c. G(x) gives you three points but for F(x) you have to use the fact that the parabola is symmetrical to get a third point.

    Since you have the point (4,2) you can deduce that there is also the point (3,2) on the graph. Now you plug in your three (x,y) pairs into the equation I wrote above and solve for your a, b and c.
    Hi Jameson, The point should be (2,2)
    Follow Math Help Forum on Facebook and Google+

  8. #8
    MHF Contributor
    Joined
    Oct 2005
    From
    Earth
    Posts
    1,599
    Quote Originally Posted by 11rdc11 View Post
    Hi Jameson, The point should be (2,2)
    Grrr, yes you're right. I wasn't looking at the graph when I typed that last response. Good catch. Thank you.
    Follow Math Help Forum on Facebook and Google+

  9. #9
    Super Member 11rdc11's Avatar
    Joined
    Jul 2007
    From
    New Orleans
    Posts
    894
    Quote Originally Posted by Jameson View Post
    Grrr, yes you're right. I wasn't looking at the graph when I typed that last response. Good catch. Thank you.
    No problem I do the same all the time lol
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. quadratic functions
    Posted in the Algebra Forum
    Replies: 4
    Last Post: May 2nd 2010, 11:04 PM
  2. Quadratic Functions
    Posted in the Algebra Forum
    Replies: 1
    Last Post: January 15th 2010, 04:10 AM
  3. quadratic functions
    Posted in the Algebra Forum
    Replies: 4
    Last Post: November 23rd 2009, 02:35 PM
  4. Quadratic Functions
    Posted in the Algebra Forum
    Replies: 16
    Last Post: July 27th 2009, 11:11 AM
  5. Quadratic functions
    Posted in the Algebra Forum
    Replies: 3
    Last Post: November 14th 2007, 06:11 PM

Search Tags


/mathhelpforum @mathhelpforum