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secondary 4 | A Maths
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Madeline
Madeline

secondary 4 chevron_right A Maths chevron_right Singapore

For part i) i got -2 and -8. Given solution k=-2. May I know why -8 is rejected? Thank you.

Date Posted: 1 month ago
Views: 41
sstrike
Sstrike
1 month ago
-8 is acceptable too
no need to rej.

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Tayng
Tayng's answer
1048 answers (A Helpful Person)
1st
Actually -8 also possible but numbers are difficult to calculate
Idk why they reject
Part 1/2
Madeline
Madeline
1 month ago
Thank you so much for your prompt response.
So -8 is also the answer? Lol...
Tayng
Tayng
1 month ago
Yeah
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Tayng
Tayng's answer
1048 answers (A Helpful Person)
There part 2/2
If you graph it -8 is also possible
K=-8 is rejected because when k=-8, y= x(x-8)^3. When k=-8, dy/dx is 0 when x=8 and not when x=2. Dy/dx=o when k=-2 when x=2. Hence, k=-2 and k=-8 is rejected.
Hope this helps.
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Erfana Beevee Binte Hassan Shariff
Erfana Beevee Binte Hassan Shariff's answer
238 answers (Tutor Details)
Madeline
Madeline
1 month ago
My dy/dx is (x+k)^2.(4x+k).
When i sub in x=2, k=-2 and x=2, k=-8, both get 0
Erfana Beevee Binte Hassan Shariff
Erfana Beevee Binte Hassan Shariff
1 month ago
Pls take a look at my working/explanation. Hope it helps. There is slightly more to do to determine the value of k in this question. For an intermediate question like this, more conditions could be placed in the question so that it is less challenging than it is supposed to be. Anyway, you have gotten the concepts of maxima and minima right, so no worries :)
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Erfana Beevee Binte Hassan Shariff
Erfana Beevee Binte Hassan Shariff's answer
238 answers (Tutor Details)
Hope this is clear.
Madeline
Madeline
1 month ago
Thank you so much, will try to understand it.
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sstrike
Sstrike's answer
5370 answers (A Helpful Person)