Maximum volume from a rectangular cardboard

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SUMMARY

The discussion focuses on maximizing the volume of a rectangular cardboard box formed by cutting squares of side length 'a' from each corner. The volume function is defined as V = (15 - 2a)(8 - 2a)a, leading to the cubic equation V = 4a^3 - 46a^2 + 120a. The first derivative, V' = 12a^2 - 92a + 120, is solved to find critical points, yielding a maximum volume at a = 1⅔. The second derivative test confirms that this critical point corresponds to a local maximum.

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Karol
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Homework Statement


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Homework Equations


First derivative=maxima/minima/vertical tangent/rising/falling
When f'(x)>0 → the function rises

The Attempt at a Solution


$$V=(15-2a)(8-2a)=4a^2-46a+120$$
$$V'=8a-46,~~V'=0\rightarrow a=5.75$$
But: ##~2a<8,~~V(a=4)=0##
So 5.75>4
And: ##~V''=8## so it holds water, it should be inverse.
 

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Karol said:
V=(15−2a)(8−2a) = 4a2−46a+120V = (15−2a)(8−2a)=4a2−46a+120​

V=(15−2a)(8−2a) ? or Volume = length x breadth ? That can't be right can it ?

How many dimensions do you need to multiply together to get the volume of a box ?
 
$$V=(15-2a)(8-2a)a=4a^3-46a^2+120a$$
$$V'=12a^2-92a+120,~V'=0\rightarrow a=1\frac{2}{3}$$
Thank you Nidum
 
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