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Graphs

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  • 30-07-2009 3:58pm
    #1
    Sully
    Moderators, Education Moderators, Technology & Internet Moderators, Regional South East Moderators Posts: 24,056 Mod ✭✭✭✭


    What's the best method for plotting graphs and picking points? Should you pick a particular group of numbers to input into the function so you can easily create the graph? Does it depend on the question you are applying a graph to?

    Usually I would have picked 1-4 negative and positive, then created a graph based on those. Just wondering should I be doing it differently?


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    #2
    RoundTower
    Registered Users Posts: 5,083 ✭✭✭RoundTower


    Sully wrote: »
    What's the best method for plotting graphs and picking points? Should you pick a particular group of numbers to input into the function so you can easily create the graph? Does it depend on the question you are applying a graph to?

    Usually I would have picked 1-4 negative and positive, then created a graph based on those. Just wondering should I be doing it differently?

    Yes you should pick a set of numbers that suits your purpose. What that set should be depends on the function and what you want to illustrate with the graph.

    For example if you wanted to graph the function ([latex]y = x^2 - 2x - 3[/latex]) you should know that this has two "roots" and a U shape. So it would be good to graph enough of the function to show the U shape and include the two roots. In this case -4 to +4 would work extremely well. On the other hand if you wanted to graph the function (y = temperature after x days of July in Dublin) your graph would be much more informative if it went from x = 0 to x = 31.

    Mostly it's common sense -- do you have a particular example you are wondering about?


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    #3
    Sully
    Moderators, Education Moderators, Technology & Internet Moderators, Regional South East Moderators Posts: 24,056 Mod ✭✭✭✭Sully


    Commonly asked to illustrate answers for slope questions on a graphc

    eg v(t)=cos(2t) + 3 t=pie/4

    or

    p(t)= -2t^2 t=k where k is a constant


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    #4
    RoundTower
    Registered Users Posts: 5,083 ✭✭✭RoundTower


    these two are slightly different because it looks like in addition to drawing a graph, you will be asked to point out on the graph the spot or spots where [latex]v(t) = \pi/4[/latex] or [latex]p(t) = k[/latex], respectively. So you should make sure to include that part on your graph.


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    #5
    Sully
    Moderators, Education Moderators, Technology & Internet Moderators, Regional South East Moderators Posts: 24,056 Mod ✭✭✭✭Sully


    Well for the first one, its just if its a stationery point (0) or not while the second is where you have to select a set of points in the first place before you even think of the graph!


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