# Rationalising the denominator Limit questionWatch

#1
So, the question is in the first line. This is my working, but apparently the answer is 1/sqrt2. Where did I go wrong and what did I do wrong? I suspect it's something from the 3rd to the 4th line. Am I suppose to rationalise the denominator at all? Or is it a different method?
0
4 years ago
#2
(Original post by Airess3)
So, the question is in the first line. This is my working, but apparently the answer is 1/sqrt2. Where did I go wrong and what did I do wrong? I suspect it's something from the 3rd to the 4th line. Am I suppose to rationalise the denominator at all? Or is it a different method?
The step where the limit sign vanishes is wrong: . (Limit sign should have remained throughout, but it's a good way to identify the line.)

Do you know L'Hôpital's rule?
0
4 years ago
#3
(Original post by Airess3)
So, the question is in the first line. This is my working, but apparently the answer is 1/sqrt2. Where did I go wrong and what did I do wrong? I suspect it's something from the 3rd to the 4th line. Am I suppose to rationalise the denominator at all? Or is it a different method?
you multiply top and bottom by the surd conjugate [2 + root(t) + (2 - root(t) ]
0
4 years ago
#4
(Original post by Hasufel)
<- what he said!

here, i think its easier to "rationalise the numerator". you end up with, before the limit

???

that is exactly what I suggested
0
4 years ago
#5
(Original post by TeeEm)
???

that is exactly what I suggested
Aherm! - my apologies. Post removed - s not neccessary afterall!
0
4 years ago
#6
(Original post by Hasufel)
Aherm! - my apologies. Post removed - s not neccessary afterall!
you did not have to remove ...
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4 years ago
#7
(Original post by TeeEm)
you did not have to remove ...
Meh! - you explained the solution needed - `nuff said!
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#8
(Original post by Smaug123)
The step where the limit sign vanishes is wrong: . (Limit sign should have remained throughout, but it's a good way to identify the line.)

Do you know L'Hôpital's rule?
No, I don't know L'Hopital's rule.
0
4 years ago
#9
(Original post by Airess3)
No, I don't know L'Hopital's rule.
look at two similar examples (with square roots) at the very last page of this booklet

0
#10

Ok, I've made amendments but I'm still stuck on what (sqrt(2-t)) x (sqrt(2+t)) = ?
0
4 years ago
#11
(Original post by Airess3)

Ok, I've made amendments but I'm still stuck on what (sqrt(2-t)) x (sqrt(2+t)) = ?
Start from the beginning

Look at post 3 and maybe post 9
0
#12
(Original post by TeeEm)
Start from the beginning

Look at post 3 and maybe post 9

But the answer is supposed to be 1/sqrt2 but I got 0?
0
4 years ago
#13
(Original post by Airess3)

But the answer is supposed to be 1/sqrt2 but I got 0?
you are applying the technique I suggested "correctly" but the multiplication which follow are all incorrect.

you must use brackets correctly
0
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