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junior college 2 | H3 Maths
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Suhaina
Suhaina

junior college 2 chevron_right H3 Maths chevron_right Singapore

I'm stuck on this qn! can help on evaluating the limit for this pls?

Date Posted: 5 years ago
Views: 427
J
J
5 years ago
Both numerator and denominator would tend to 0, resulting in 0/0 which makes it undefined/indeterminate

So we use L'Hopital's rule here, where

lim [ f(x)/g(x) ] = lim [f'(x)/g'(x)]


You should be getting 16/27 as the limit if done correctly.

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Eric Nicholas K
Eric Nicholas K's answer
5997 answers (Tutor Details)
1st
One way to do this is what we call the L Hopital Rule, which is applied when the limit form after substitution is like 0/0 or infinity/infinity.

In such situations, the rule lets us differentiate both the top and numerator in the hope that the new value obtained is able to be calculated.
Suhaina
Suhaina
5 years ago
sorry is there any way to do this without the LHopital rule?
Eric Nicholas K
Eric Nicholas K
5 years ago
I did think of introducing the conjugate of the denominator at first and that was my first approach, but it led to a big mess.

If I manage to find a way, I will post a new one here.

EDIT: Found.
Eric Nicholas K
Eric Nicholas K
5 years ago
Sent in the alternative approach already
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Eric Nicholas K
Eric Nicholas K's answer
5997 answers (Tutor Details)
I found an alternative. We must do double conjugate. One for the numerator and one for the denominator.

I presume you are able to factorise the resulting denominator’s (x3 - 3x - 2) by Guess and check and Long division.
Eric Nicholas K
Eric Nicholas K
5 years ago
The x - 2 expression which I have found in the middle of my workings is the root cause of why the fraction becomes 0/0. Once this is eliminated, there will no longer be any x - 2 present in the denominator and all other expressions there cannot be zero, so we obtain a nice number.
Suhaina
Suhaina
5 years ago
Now I understand how to do this question. Thank you so much for your help!