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    Hey,
    I've been trying to get this optimisation question.
    I've got the answer to (b), but cannot for the love of me get part (a) :p:

    Could someone give me some hints as to how you get it? :p:

    Thanks!
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    try to get the height in terms of x.

    if you're still struggling:
    Spoiler:
    Show
    inner surface area = 2 sides + 2 sides + bottom
    12=2(2xh)+2(xh) + 2x^2

    then V=lbh
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    For part b, do you just differentiate?
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    (Original post by Dado Prso)
    try to get the height in terms of x.

    if you're still struggling:
    Spoiler:
    Show
    inner surface area = 2 sides + 2 sides + bottom
    12=2(2xh)+2(xh) + 2x^2

    then V=lbh
    Hey,
    I managed to get the surface area earlier... but just can't work out the next bit :p:
    Still can't get it :o: How I hate the first bit of these questions!
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    (Original post by CT_Scan)
    For part b, do you just differentiate?
    Yeah, then nature table.
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    (Original post by FuturePilot)
    Yeah, then nature table.

    Yeah, thanks for reassuring me. I am sorry but I cannot help you with the first part, have you had your prelim yet? Mines is tomorrow. :eek:
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    Part b:

    Differentiate

    Nature Table

    Equate to 0

    Then Solve

    Methinks
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    (Original post by FuturePilot)
    Hey,
    I managed to get the surface area earlier... but just can't work out the next bit :p:
    Still can't get it :o: How I hate the first bit of these questions!
    rearrange the surface area equation to get (6-x^2)/3x=h

    v=lbh
    v=2x^2 x (6-x^2/3x)

    v=2x^2/3x x (6-x^2)

    v=2x/3 (6-x^2) as required.
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    (Original post by CT_Scan)
    Yeah, thanks for reassuring me. I am sorry but I cannot help you with the first part, have you had your prelim yet? Mines is tomorrow. :eek:
    No bother. Oh, good luck! Mine's on Friday
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    Could someone help me with this one?

    f(x) = 4x^2 - 14x +24

    It was in our prelim and we had to find the answer which minimizes the function.

    I think I did it the right way but I don't know if I got the right answer?
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    (Original post by Lulope)
    Could someone help me with this one?

    f(x) = 4x^2 - 14x +24

    It was in our prelim and we had to find the answer which minimizes the function.

    I think I did it the right way but I don't know if I got the right answer?
    f'(x) = 8x - 14

    f'(x) = 0 at sps,
    8x = 14
    x = 7 / 4

    (this is clearly going to be the minimum, since there aren't any other sps!)

    f(7 / 4) = 4(49/16) - 14(7/4) + 24 = 49 / 4 - 49 / 2 + 24 = 0.25(49 - 98 + 96) = 47 / 4

    (\frac{7}{4}, \frac{47}{4}) is the minimum tp of f.

    (The way you've worded it sounds like you only needed x = 7 / 4 as the answer, though)
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    (Original post by TheUnbeliever)
    f'(x) = 8x - 14

    f'(x) = 0 at sps,
    8x = 14
    x = 7 / 4

    (this is clearly going to be the minimum, since there aren't any other sps!)

    f(7 / 4) = 4(49/16) - 14(7/4) + 24 = 49 / 4 - 49 / 2 + 24 = 0.25(49 - 98 + 96) = 47 / 4

    (\frac{7}{4}, \frac{47}{4}) is the minimum tp of f.

    (The way you've worded it sounds like you only needed x = 7 / 4 as the answer, though)
    Thank you!

    I have a horrible feeling I integrated instead of differentiating :facepalm2:
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    -differentiate and make equal to zero for x.
    -find the second derivative (so differentiate again)
    -substitute in x to the second derivative and if your answer is negative, it gives a Maximum
    .
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    7 years later ... they have probs got their degree now hahah
 
 
 
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