Definite integral doubt.......

Given, (LL=f(y),UL=f(x))∫et dt = (LL=y,UL=x) ∫1/t dt, for all x,y belonging to (1/e2,∞) where f is continuous and differentiable function and f(1/e)=0.
If g(x)={ ex, x≥k
{ ex2, 0<x<k
Find k such that f(g(x)) is continuous for all x>0.

20 Answers

62
Lokesh Verma ·

hmm.. ok

I think there is a mistake in typing or something's still missing cos of partial typing!

11
Shailesh ·

I like this one concept..

Good

Thank you abhishek and nishant for the question and solution...

33
Abhishek Priyam ·

Ok.........

62
Lokesh Verma ·

exactly..

no a,b,c,d....
just take their integrals..

and after taht..value 0 and 1!

take teh difference..

62
Lokesh Verma ·

yeah i knew this is the doubt u will have..

give me 1 sec.. i will post another image :)

33
Abhishek Priyam ·

Or we have only one choice evaluate the indefinite by parts and take limits at last.

33
Abhishek Priyam ·

33
Abhishek Priyam ·

got it...... problem was in (0,1)

62
Lokesh Verma ·

x<0 it is 1/3-x/2
x>1 it is x/2-1/3
in between it is x3/3+1/3-x/2

the trick is that in between (0,1) case c above.. in my post..

u should take integral as sum of integrals from (0,x) and from (x,1)

May be i made some error in the calculation.. but the basic idea is correct... if u do get some different answer tell me.. i will try to correct it :)

33
Abhishek Priyam ·

Ok i am trying.....

33
Abhishek Priyam ·

(LL= ,UL= )is lower and upper limit respectively

62
Lokesh Verma ·

Q2

we have to take 3 cases:

a) x<0
b)x>1
c) x ε [0,1]

I hope this is a hint! But i will try to post the graph right away!

I hope u guys try to get the middle paths

33
Abhishek Priyam ·

pata nahi i'm also getting nothing it is in CPP of FIITJEE sir, which i'm solving

62
Lokesh Verma ·

if is a continuous fn for all x except 0 and (LL=0,UL=a)∫f(x)dx=b

If g(x)=(LL=x,UL=a)∫f(t)/t dt, then express (LL=0,UL=a)∫g(x)dx in terms of b

yaar this question does not seem to make too much sense to me!!

Why? bcos we know nothing about f(x)!

Case I
say a=1

f(x)={x} {fractional part of x}

Case II

a=1
f(x) = 1-{x}

B is same for both these cases!

33
Abhishek Priyam ·

that k comes out to be 1 in q.1

33
Abhishek Priyam ·

Q.2 Let f(x)= (LL=0,UL=1)∫|t-x|*t dt for all real x. Sketch the graph of f(x) and what is the min value of f(x).

33
Abhishek Priyam ·

f is a continuous fn for all x except 0 and (LL=0,UL=a)∫f(x)dx=b

If g(x)=(LL=x,UL=a)∫f(t)/t dt, then express (LL=0,UL=a)∫g(x)dx in terms of b

62
Lokesh Verma ·

hmm.. i understand what "inspires" u to do differentiate.....

But i strongly think this is not needed in this question...

The first look does not make me feel that there will be different results!
But i am not sure.. i ll check and see :)

33
Abhishek Priyam ·

what if i differenciate both side of (LL=f(y),UL=f(x))∫et dt = (LL=y,UL=x) ∫1/t dt wrt x then what we will get ...

62
Lokesh Verma ·

Hey priyam, have u figured out what f(x) is?

This is simple to do using y=1/e

and the limit of integral from 1/e to x!
so u will get f(x)

The 2nd part is finding k...

If this is the actual blocking point then i will tell u that part as well :)

Your Answer

Close [X]