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    Hey I have a question for Core 1 for Edexcel.

    I dont understand the "hint".








    how was i supposed to know that "The minimum point on y=(x-2)(x+2)^2 is less than -8." ?. If i knew this my sketch would have looked different and i would have got the marks . but because my minimum point on y=(x-2)(x+2)^2 was -8 and not less than -8. therefore my intersectons were wrong.

    this is my sketch (obviously it was neater but i used paint which i find hard to use)



    so my question is how was i supposed to know that "The minimum point on y=(x-2)(x+2)^2 is less than -8." ?

    thanks (sorry if its confusing)
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    In this question, you should use the hint given to get the required minimum point. However if you're not given a hint then when sketching curves it's often a good idea to differentiate them yourself to get maximum/minimum points.
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    the book has nothing on minimum and max point infact it says at one point you dont have to calculate them?

    v confused.
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    (Original post by jayseanfan)
    the book has nothing on minimum and max point infact it says at one point you dont have to calculate them?

    v confused.
    You don't always have to calculate minimum/maximum points since often it's pretty clear roughly where they should be. However if the question asks you to calculate them or if their position makes a substantial difference to the shape of the graph (like in this question) then you should calculate them. If in doubt, calculate them but if you're running out of time, don't bother.
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    how do you u calculate the min and max point then?

    im a bit annyoyed because i got the question wrong after following the exact same method they suggested and the only reason i got it wrong was i didn't calculate the max and min point , which i wasn't going to since the book told me spefically it wasn't a requirement
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    differentiate and then make it equal 0 (bacause the gradient is 0 at max n mins) and the if you differentiate again it'll give tell you whether it's max or min or inflection - substitute x and if it's more than 0 it's minimum, less than 0 it's maximum and equals 0 it's point of inflection (where it turns like on x^3 graph)
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    (Original post by jayseanfan)
    how do you u calculate the min and max point then?

    im a bit annyoyed because i got the question wrong after following the exact same method they suggested and the only reason i got it wrong was i didn't calculate the max and min point , which i wasn't going to since the book told me spefically it wasn't a requirement
    I haven't seen your textbook but I think what it probably means is that in simple cases you don't need to calculate minimum/maximum points but in a question like this where it's more complicated, you do need to calculate them.

    I suppose one way of telling when you need to calculate them is whenever you do the sketch and draw on minimum point, ask yourself whether you're sure it goes above or below some other line on your graph. For example if you're sketching y=x^2 +1 then obviously the minimum point is above the x axis so you don't need to calculate that. But if you're sketching y=x(x-1) and y=-x on the same axes, you would know that the minimum point of the curve would go below the x axis but you wouldn't be sure if the curve goes above or below y=-x. In this case you would want to calculate the minimum point.
 
 
 
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