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Ordinary Maths Help

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  • 07-06-2010 7:57pm
    #1
    kev9100
    Registered Users Posts: 1,271 ✭✭✭


    Sorry for the really basic question but I really struggle with maths. How do you find the max/min of a line? Cheers.


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    #2
    Samskeyti
    Banned (with Prison Access) Posts: 30 ✭Samskeyti


    I assume you mean in the differentiation question? If it's like part iii of question 8, 2008. Then you differentiate the given function, solve the resulting quadratic, and sub both of your answers back into the original equation to get the Y value. Then plot the two points on a graph.


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    #3
    ldxo15wus6fpgm
    Closed Accounts Posts: 1,359 ✭✭✭ldxo15wus6fpgm


    For the max/min you need to differentiate the function (find DY/DX)

    Next, you let DY/DX = 0 and solve the equation

    for each value of x you put it back into the original equation (which equals y) to find that x value's relative y value. You will end up with two sets of co-ordinates, they are your turning points.


    The equation you are given in the question should be the one which equals y. If it has f(x) = whatever, that's the same thing as saying y = whatever.


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    #4
    Reillyman
    Closed Accounts Posts: 834 ✭✭✭Reillyman


    Don't forget to get [latex] d^2y/dx^2[/latex] and plug in the [latex]x[/latex] values into the answer. If the result is +...Min and if it's -...Max


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    #5
    Gael23
    Registered Users Posts: 12,118 ✭✭✭✭Gael23


    This is NOT the ideal way to do it but you can draw the graph first then you can see the max/min point on it.


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    #6
    Reillyman
    Closed Accounts Posts: 834 ✭✭✭Reillyman


    ryanf1 wrote: »
    This is NOT the ideal way to do it but you can draw the graph first then you can see the max/min point on it.

    Okay I don't know how much time ye have for the OL exam but seriously DO NOT do this. The time it'll take to draw a graph, and even then you would have to do it extremely accurate to get the precise max/min. You'll get no attempt marks whatsoever if it's wrong and only a small amount even if you get it right.


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    #7
    Gael23
    Registered Users Posts: 12,118 ✭✭✭✭Gael23


    Well you have to draw a graph in the next part anyway.


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    #8
    ldxo15wus6fpgm
    Closed Accounts Posts: 1,359 ✭✭✭ldxo15wus6fpgm


    ryanf1 wrote: »
    Well you have to draw a graph in the next part anyway.

    You need to do a graph with about 10 points. You'd need to make out way more points to get an accurate co-ordinate for each max/min. However depending on your level of maths you could do it this way if you were really stuck, but obviously leave it till the end.


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    #9
    Reillyman
    Closed Accounts Posts: 834 ✭✭✭Reillyman


    Yeah definitely, you'd need to to out so many points to get a precise x value. tbh I can't see what's wrong with the normal way, it's so simple?


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