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a level maths C1

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    Help please someone tell me how to do inequalities and also tell me how you know the sign is < or > . For example, x^2 -11x+24<0, why is the answer 3<x<8 and how do you do it please !!!!!! anwer
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    (Original post by Mr revision)
    Help please someone tell me how to do inequalities and also tell me how you know the sign is < or > . For example, x^2 -11x+24<0, why is the answer 3<x<8 and how do you do it please !!!!!! anwer
    You sketch the graph and look for the points where y < 0 or y> 0 etc.



    For what values of x is the y value less than 0?
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    (Original post by Mr revision)
    Help please someone tell me how to do inequalities and also tell me how you know the sign is < or > . For example, x^2 -11x+24<0, why is the answer 3<x<8 and how do you do it please !!!!!! anwer
    You have to find the critical values.

    x^2 - 11x + 24 factorises to (x-3)(x-8)

    draw that curve and look for the region where y is less than 0.
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    (Original post by SeanFM)
    You sketch the graph and look for the points where y < 0 or y> 0 etc.



    For what values of x is the y value less than 0?
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    i was going to answer that
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    you always hack on maths threads :emo:
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    jokes :lol:
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    no i wasn't :fuhrer:
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    (Original post by Mr revision)
    Help please someone tell me how to do inequalities and also tell me how you know the sign is < or > . For example, x^2 -11x+24<0, why is the answer 3<x<8 and how do you do it please !!!!!! anwer
    first, set  \displaystyle x^2 - 11x + 24 = 0 and solve for x to find critical values.

    when you do this youll get x = 3 or x = 8.

    From here you need to work out whether the curve is less than 0 for 3<x<8 or x<3 U x>8. To do this you have two choices;

    Sketch it - you can see that the quadratic has a y intercept of 24 so you know three points on the curve are (0,24), (3,0) and (8,0). You also know this quadratic has a U shape so a quick sketch will tell you that  \displaystyle x^2 - 11x + 24 &lt; 0 for values 3 < x < 8.

    Or you can sub in some values - sub in x = 0, x = 5 and x = 10 for example and youll see that f(0) >0, f(5) < 0 and f(10) > 0 therefore the function is <0 for values 3<x<8
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    Thank you all but how do you look for the region where y>0 or y<0
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    (Original post by NotNotBatman)
    You have to find the critical values.

    x^2 - 11x + 24 factorises to (x-3)(x-8)

    draw that curve and look for the region where y is less than 0.
    Thanks but how do you look for the region where y is less than 0
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    (Original post by Mr revision)
    Thanks but how do you look for the region where y is less than 0
    All the points of the curve below the x axis. If you look at the graph SeanFM posted, y=0 on the x axis, so at x=3 and x=8, anything below that is where y<0 and anything above is where y>0.
 
 
 
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