Ask Singapore Homework?
Upload a photo of a Singapore homework and someone will email you the solution for free.
Question
secondary 4 | A Maths
2 Answers Below
Anyone can contribute an answer, even non-tutors.
Good evening Mr Eric, could you kindly advise on how to find f’(x) where a and b are constants? Many thanks!
Date Posted: 3 years ago
Views: 345
try to simplify your expression first before you try to differentiate.
in this case f(x) simplifies to pi * exp( (-1/3)a),
which is effectively a constant (there is no 'x' in the expression).
differential of a constant is 0
therefore f'(x) = 0
in this case f(x) simplifies to pi * exp( (-1/3)a),
which is effectively a constant (there is no 'x' in the expression).
differential of a constant is 0
therefore f'(x) = 0
Hi Mr Chau, with both Mr Eric and Mr Tan's advice. I strongly believe that the model answer given to me for this question is incorrect. Thus, your advised solution is right which is also what I have derived :D
Thank you and have a good day.
Thank you and have a good day.
See 2 Answers
done
{{ upvoteCount }} Upvotes
clear
{{ downvoteCount * -1 }} Downvotes
Always try to simplify the expression before differentiation - Grandmaster Eric's sidekick.
Date Posted:
3 years ago
Thanks for the advice, Mr Tan.
I got the same answer but it wasn't the right answer (I am assuming that the model answer given is correct).
I got the same answer but it wasn't the right answer (I am assuming that the model answer given is correct).
It does happen that model answers are incorrect. Or there was a mistake made during the proofreading and editing of the question. Post the answer - one can often work backwards to elucidate the intended question.
Hi Mr Tan, the model answer is Pi e^-a/3 (b-1).
Candice, I tried plotting the graph of f(x) on Desmos as well but obtained the expected - a horizontal line.
Candice, the model answer looks fishy. The derivative of e^f(x) always contains some expression containing x within the power, the most basic of which is e^x which is invariant after differentiation.
I tried eliminating the "b" in the denominator, but obtained another expression
f(x) = π times e^(-a/3) times e^[(b - 1) x]
which differentiates to the same expression as above, multiplied by a factor (b - 1).
In this case, the e^[(b - 1) x] remains present. Or put it simply, even the letter "x" should survive, but the model answer seems to miss out the letter "x".
I tried eliminating the "b" in the denominator, but obtained another expression
f(x) = π times e^(-a/3) times e^[(b - 1) x]
which differentiates to the same expression as above, multiplied by a factor (b - 1).
In this case, the e^[(b - 1) x] remains present. Or put it simply, even the letter "x" should survive, but the model answer seems to miss out the letter "x".
Hi Mr Tan, with both Mr Eric and Mr Chau's advice. I strongly believe that the model answer given to me is incorrect. You are right :)
Thank you for your feedback and have a good day ahead.
Thank you for your feedback and have a good day ahead.
done
{{ upvoteCount }} Upvotes
clear
{{ downvoteCount * -1 }} Downvotes
Good evening Candice! I just had some free time to look at this question. I also obtained 0 as my final answer.
Date Posted:
3 years ago
Good morning Mr Eric :)
Thank you so much for your assurance coz I have worked on this question for many times and still got 0 as my final answer too which is very different from the model answer given to me.
Yes, I strongly believe that you are correct! Like what Mr Tan has mentioned, sometimes model answer can be incorrect. I just don't have the confident to challenge it :(
Once again thank you very much for coming back to me, and I really appreciate your advice and valuable feedback as always.
I hope you have a good day ahead :D
Thank you so much for your assurance coz I have worked on this question for many times and still got 0 as my final answer too which is very different from the model answer given to me.
Yes, I strongly believe that you are correct! Like what Mr Tan has mentioned, sometimes model answer can be incorrect. I just don't have the confident to challenge it :(
Once again thank you very much for coming back to me, and I really appreciate your advice and valuable feedback as always.
I hope you have a good day ahead :D
360 Tutoring Program