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question on maximisation and minimisation in geometry (1 Viewer)

waltssillyhat

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please help with part b!! this is part of curve sketching using the derivative
 

C2H6O

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Find dA/dy using product rule and chain rule, treat r as constant, find the value of y where A is max. sub that value of y into the area formula
 

C2H6O

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Oh btw you don't need to sketch anything just set dA/dy as equal to 0 to find stationary points and solve algebraically, remembering that r and y are positive numbers
 

waltssillyhat

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Oh btw you don't need to sketch anything just set dA/dy as equal to 0 to find stationary points and solve algebraically, remembering that r and y are positive numbers
do i have to find the second derivative to test if there is a maximum turning point when dA/dy is equal to 0?
 

C2H6O

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do i have to find the second derivative to test if there is a maximum turning point when dA/dy is equal to 0?
You mean in case it’s a minimum turning mount instead of a max? No because it works out that way, and you only get 1 answer. Also you could sub it in and you already know what the correct answer is, so if you get that you’re good.
 

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