SPM - Add Maths - Form 4 - Differentiation (Maximum Area)

This is one of the famous type question in the form 4, differentiation chapter. The question will always ask you find the maximum area, or maximum volume, or maximum radius and so forth. Therefore, hope this question will give you some basic idea on how to solve this kind of questions.
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[@yunling4411]

But liek sir, shouldn't we get D2A/DX2 then only get max =0?how come it is DA/DX=0

[@金银大帝]

d/dx = m. if max//min，m = 0

[@nazmahrauf7959]

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