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very simple graph question

  • 05-12-2007 10:16pm
    #1
    jtiernan
    Closed Accounts Posts: 192 ✭✭


    graphwi7.th.jpg

    I understand f(x) = x 0<x<2
    just not y=-x/2+3

    How did they get that?


Comments

  • #2
    chris85
    Registered Users, Registered Users 2 Posts: 4,502 ✭✭✭chris85


    jtiernan wrote: »
    graphwi7.th.jpg

    I understand f(x) = x 0<x<2
    just not y=-x/2+3

    How did they get that?

    y=-x/2+3 is the equation of the line that goes from the point (2,2) to the point (6,0).

    Get the slope, m using m=(y2-y1)/(x2-x1)

    Then get equation of line using y-y1=m(x-x1)


  • #3
    Fremen
    Registered Users, Registered Users 2 Posts: 2,481 ✭✭✭Fremen


    You can also check that the equation of that line is correct by subbing in x = 2 and x = 6 into the equation. You'll get y = 2 and y = 0 as expected.

    On a side note, whatever twat drew that graph left it undefined at x = 2. It should read "f(x) = 2, x less than or equal to 2."

    Bloody innumerate examiners.


  • #4
    jtiernan
    Closed Accounts Posts: 192 ✭✭jtiernan


    :D thanks lads


  • #5
    MathsManiac
    Registered Users, Registered Users 2 Posts: 1,595 ✭✭✭MathsManiac


    Fremen wrote: »
    You can also check that the equation of that line is correct by subbing in x = 2 and x = 6 into the equation. You'll get y = 2 and y = 0 as expected.

    On a side note, whatever twat drew that graph left it undefined at x = 2. It should read "f(x) = 2, x less than or equal to 2."

    Bloody innumerate examiners.

    ...and also undefined at x=0

    ...and therefore, of course, undefined at infinitely many points!


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