23-01-2009 Proof of LH Rule

Give the proof of LH rule when f(a)=0 and g(a)=0

f(x) is the numerator and g(x) is the denominator...

Trust me it is not very difficult..

Use the basic definition of Derivative...

(Sorry mistake galti ho gaya.)

16 Answers

24
eureka123 ·

33
Abhishek Priyam ·

f(x) is the numerator and g(x) is also the numerator... [7]

24
eureka123 ·

I think there is a mistake in question

24
eureka123 ·

but sir why would we apply LH rule then?????????????????because it wont be indeterminate then.....

33
Abhishek Priyam ·

Yes that should be a mistake...i think

1
skygirl ·

then he wudn hav written 'also' ...

33
Abhishek Priyam ·

hmm...

1
mkagenius ·

if both are in num. then the limit should be 0 :) what was to prove...........?........?....?

62
Lokesh Verma ·

sorry galti ho gaya...

bhawna ko samjo ;)

aise haan this was not the proof i was looking for eureka.. but still this is good enuf...

There is a more "elegant" proof...

33
Abhishek Priyam ·

If we take derivative of both num and den... we cancel 0 making factor.. if both have only one root at that pt... diff 1nce is enough if two repeated roots then f'(x) will have one root so f'(a) will be also 0 so we have to diff again ...

11
Subash ·

Ltx→af(x)/g(x) =Lt h→0 f(a+h)/g(a+h)

=Lth→0 f(a+h)-f(a)/g(a+h)-g(a) ((using g(a)=f(a)=0))

=Lth→0 (f(a+h)-f(a)/h)/(g(a+h)-g(a)/h)

=Lt x→a f'(x)/g'(x)

11
Subash ·

was this what u where expecting or r u expecting some thing other than this

1
skygirl ·

bhaiya aap aise 'also' likhke bhawnao ko zaahir kiye ki hum sab samajh ke bhi soch rahe the ... ki jo hum samjhe woh hume nahi samajhna chaiye tha.. [3] [3]

1
rahul wadhwani ·

kya mast shayari padete hi hum bhool gaye ham kya karne aaye the aur kya gaye waah!waah!waah!waah!waah!waah!waah!waah!waah!waah!waah!waah!waah!waah!waah!waah!waah!waah!waah!waah!waah!

11
Subash ·

is there any other proof for this

62
Lokesh Verma ·

no this is the proof I was looking for ;)

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