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secondary 4 | A Maths
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Pls help idk how to find DA/Dr thx
Date Posted: 8 months ago
Views: 145
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Hello, for such rate of change questions, after differentiating A with respect to r to get dA/dr, you will need to substitute a specific value of r (usually given in the question) to find a specific numerical value for dA/dr. After differentiating A wrt r, what you get is a function of x, meaning the rate of change of A is dependent on the value of r. Therefore to evaluate it always remember to substitute the given value of r in to get the dA/dr value at the instant when r takes that specific value. Subsequently, use the chain rule formula (which you have written at the side, good job) to find dA/dt. Hope this helps! Leave a comment if you still need help / clarifications!
Date Posted:
8 months ago
Can I know where did I do wrong for my differentiate
Hello, it seems like you know that you have to apply product rule formula for differentiation, but there were errors made in the process. In the second line of your differentiation, you evaluated d/dr (4 + r^2)^1/2 as (1/2)(4 + r^2)^-1/2(r^2). But this should be (1/2)(4 + r^2)^-1/2(2r). Go back to differentiation basics - differentiate 4 + r^2 should give you 2r not r^2. Secondly, in the later part of the same line, d/dr (pi r) was evaluated as pi r, but this should be pi only. The last line in the differentiation has many algebraic simplification errors - you can try correcting the second line first and then slowly simplify the expression, and you should be able to get what I wrote down for you. Hope this helps! Leave a comment if you still need help.
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