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    *pic below*

    could someone please tell me how to make x the subject? I've been trying for ages. Trying to make dA/dx = 0 so only the top part = 0 and just stuck
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    any help is appreciated
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    Is that the whole question?
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    (Original post by zezno)
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    could someone please tell me how to make x the subject? I've been trying for ages. Trying to make dA/dx = 0 so only the top part = 0 and just stuck
    (Original post by zezno)
    any help is appreciated
    What's the actual question?? Sure you can make the differential equal 0 to find the points where A is minimised/maximised.

    In which case you have

    48x^2+x(x^2-50)\sqrt{100-x^2}-2400=0

    \Leftrightarrow 48x^2-2400 = -x(x^2-50)\sqrt{100-x^2}

    and note that 48x^2-2400=48(x^2-50) then carry on from there.
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    (Original post by RDKGames)
    What's the actual question?? Sure you can make the differential equal 0 to find the points where A is minimised/maximised.

    In which case you have

    48x^2+x(x^2-50)\sqrt{100-x^2}-2400=0

    \Leftrightarrow 48x^2-2400 = -x(x^2-50)\sqrt{100-x^2}

    and note that 48x^2-2400=48(x^2-50) then carry on from there.

    I always get stuck when there's more than 1 x term with powers involved.

    So I noticed that you can cancel out the (x^2 -50) which gave me:

    -x(100-x^2)^1/2 = 48

    I tried getting rid of the square root so now:

    -x(100-x^2) = 2304

    expanding

    -100x + x^3 = 2304

    and yeah stuck lol two x's, factorising would give me though:

    x(-100+x^2) = 2304
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    (Original post by zezno)
    I always get stuck when there's more than 1 x term with powers involved.
    ...

    I tried getting rid of the square root so now:

    -x(100-x^2) = 2304

    ...
    This should be x^2(100-x^2)=2304
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    (Original post by RDKGames)
    This should be x^2(100-x^2)=2304
    ah okay. Then what next?
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    (Original post by zezno)
    ah okay. Then what next?
    Achieve the form x^4+bx^2+c=0 then you have a quartic which you can treat as a quadratic with a simple substitution X=x^2 and solve for X by solving the quadratic then solve for x itself.
 
 
 
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