$\"\"$

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Observe the figure the trough is $\"\"$ long and $\"\"$ across the top.

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And the side of isosceles triangle is $\"\"$ .

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(a).

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The equation for the volume is $\"\"$ .

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From the figure $\"\"$ ,there fore $\"\"$

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Apply derivative on each side with respect to $\"\"$ .

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$\"\"$

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$\"\"$

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Find $\"\"$ ,when $\"\"$ and $\"\"$ .

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$\"\"$

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$\"\"$ .

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$\"\"$

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(b).

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$\"\"$

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Find $\"\"$ and $\"\"$

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$\"\"$

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i.e $\"\"$ and $\"\"$ .

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Substitute the above values into $\"\"$ .

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$\"\"$

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$\"\"$ .

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$\"\"$

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(a). $\"\"$

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(b). $\"\"$ .