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# Volume of a Box

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Why bother with a post grad course - waste of time? 17-10-2016
1. Yo guys,

Any help would be gratefully appreciated! Dunno if im making a stupid mistake and not seeing it or the answers wrong.. :L most likely the first case!

Im doing Question 2, and heres my working out:

sides of the box will be (6-x) as ive labelled. Making the total Volume of the box to be V=(6-x)(6-x)x which expanded out becomes V=x^3 - 12x^2 + 36x

differentiate that and you get dV/ds = 3X^2 - 24x + 36. Then find the stationary points, of which the maximum would be the largest volume possible point and hence the corresponding x value, which according to the question should be 1.

so you i found two stationary points, x=6 and x=2, plugging them in you see that x=2 is the maximum stationary point. pretty obvious i know when ofc if x=6, the volume would be zero.

but then this means the max volume would be if x=2 in the diagram, not x=1 like the answers suggests...? ive even plugged x=2 and x=1 into my original V (volume) equation and it shows x=2 producing a larger volume... so is there something wrong with me volume equation?

Please help TSR community... *echo community*

Cheers
2. (Original post by trm1)
Yo guys,

Any help would be gratefully appreciated! Dunno if im making a stupid mistake and not seeing it or the answers wrong.. :L most likely the first case!

Im doing Question 2, and heres my working out:

sides of the box will be (6-x) as ive labelled. Making the total Volume of the box to be V=(6-x)(6-x)x which expanded out becomes V=x^3 - 12x^2 + 36x

differentiate that and you get dV/ds = 3X^2 - 24x + 36. Then find the stationary points, of which the maximum would be the largest volume possible point and hence the corresponding x value, which according to the question should be 1.

so you i found two stationary points, x=6 and x=2, plugging them in you see that x=2 is the maximum stationary point. pretty obvious i know when ofc if x=6, the volume would be zero.

but then this means the max volume would be if x=2 in the diagram, not x=1 like the answers suggests...? ive even plugged x=2 and x=1 into my original V (volume) equation and it shows x=2 producing a larger volume... so is there something wrong with me volume equation?

Please help TSR community... *echo community*

Cheers
Scratch all that lol... realised the formula for volume should be (6-2x) not (6-x)... im gunna go ahead and blame the fact ive been working since 7am is the cause of this

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