Results 1 to 10 of 10

Math Help - Graphing

  1. #1
    Senior Member
    Joined
    Jul 2007
    Posts
    290

    Graphing

    I forgot how to graph these types of equations without a calculator. Can someone give me a quick rundown?

    x = y - y^2

    Thanks
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Senior Member
    Joined
    Jul 2007
    Posts
    290
    also how would I graph this with my ti-89?
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Super Member
    Joined
    Jun 2008
    Posts
    792
    x = y - y^2

    This is the inverse function of a parabola. Consider the following equation:
    x - h =  \frac1{4p} (y-k)^2

    The vertex is: V(h, k)
    And the need for p is to know if the function opens lefts or opens right (since this is an inverse of a parabola). Basically, if p>0, it opens right. If p<0, it opens left.

    Now, first, we have to complete the square:

    Rearrange the equation first:
    Take -1 as common factor: x = - (y^2 - y)
    Complete the square: x = - (y^2 - y + \frac1{4} - \frac1{4})
    Take -1/4 out by multiplying it with -1: x = - (y^2 - y + \frac1{4}) + \frac1{4}
    Factor the completed square: x = - (y-\frac1{2})^2 + \frac1{4}
    x - \frac1{4} = - (y-\frac1{2})^2

    Does this equation look familiar?
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Forum Admin topsquark's Avatar
    Joined
    Jan 2006
    From
    Wellsville, NY
    Posts
    9,838
    Thanks
    320
    Awards
    1
    Quote Originally Posted by JonathanEyoon View Post
    I forgot how to graph these types of equations without a calculator. Can someone give me a quick rundown?

    x = y - y^2

    Thanks
    Quote Originally Posted by JonathanEyoon View Post
    also how would I graph this with my ti-89?
    y^2 - y - x = 0

    From the quadratic formula:
    y = \frac{1 \pm \sqrt{4x + 1}}{2}

    As you can see this is not a function. So you have to make two graphs, one using the + sign and one using the - sign.

    -Dan
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Senior Member
    Joined
    Jul 2007
    Posts
    290
    Thanks alot guys. I appreciate it
    Follow Math Help Forum on Facebook and Google+

  6. #6
    Moo
    Moo is offline
    A Cute Angle Moo's Avatar
    Joined
    Mar 2008
    From
    P(I'm here)=1/3, P(I'm there)=t+1/3
    Posts
    5,618
    Thanks
    6
    Hello,

    Quote Originally Posted by JonathanEyoon View Post
    also how would I graph this with my ti-89?
    You can use the graph with parameters (in MODE, choose the function mode to "parametric")

    Then, y1=t and x1=t-t^2

    Follow Math Help Forum on Facebook and Google+

  7. #7
    Senior Member
    Joined
    Jul 2007
    Posts
    290
    wow thanks for the tip. Question. I set my 89 to parametric and input what you said but i'm only getting the top half of the graph. How do I make it so I get the both the top and bottom?
    Follow Math Help Forum on Facebook and Google+

  8. #8
    Moo
    Moo is offline
    A Cute Angle Moo's Avatar
    Joined
    Mar 2008
    From
    P(I'm here)=1/3, P(I'm there)=t+1/3
    Posts
    5,618
    Thanks
    6
    Quote Originally Posted by JonathanEyoon View Post
    wow thanks for the tip. Question. I set my 89 to parametric and input what you said but i'm only getting the top half of the graph. How do I make it so I get the both the top and bottom?
    Ha ! I found the problem !!!

    You have to take negative values of y.

    So in the window (diamond F2), configurate the t.
    Here is what I've done :

    tmin=-10
    tmax=10
    tstep=.1
    xmin=-10
    xmax=10
    xscl=1
    ymin=-10
    ymax=10
    yscl=1


    When you graph it, you can increase the speed by increasing tstep (to .5 for example).
    Then, the usual stuff, when you're in the graph window, do F2 - A to get an automatic zoom
    Follow Math Help Forum on Facebook and Google+

  9. #9
    Senior Member
    Joined
    Jul 2007
    Posts
    290
    Thanks alot! Very much appreciated!
    Follow Math Help Forum on Facebook and Google+

  10. #10
    Super Member
    Joined
    Oct 2007
    From
    London / Cambridge
    Posts
    591
    Quote Originally Posted by JonathanEyoon View Post
    Graph the curve with equation:
    x = y - y^2<br />
    Why not first sketch this graph on the y-x plane? as this sketch is very easy, then all you need to do is swap around the y and x axis to et your sketch in the x-y plane, this can be achieved easily by reflecting your graph in the line y=x.

    Bobak
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. graphing
    Posted in the Algebra Forum
    Replies: 6
    Last Post: May 19th 2011, 05:43 AM
  2. Graphing
    Posted in the Math Topics Forum
    Replies: 1
    Last Post: May 23rd 2009, 05:31 PM
  3. graphing of sin and cos
    Posted in the Pre-Calculus Forum
    Replies: 4
    Last Post: October 28th 2008, 09:50 AM
  4. Graphing
    Posted in the Trigonometry Forum
    Replies: 3
    Last Post: January 16th 2008, 11:18 AM
  5. help with graphing
    Posted in the Pre-Calculus Forum
    Replies: 1
    Last Post: December 9th 2007, 09:23 AM

Search Tags


/mathhelpforum @mathhelpforum