Chalte Chalte weird limit

find the Domain and Range(of course give explanation)these are also last yrs question

1)f(x)=limn->∞cos(n! 2Πx)
2)g(x)=limn->∞cosn( 2Πx)
3)h(x)=limn->∞{cos(nx) + 2}1/n

7 Answers

24
eureka123 ·

these were done some time back in forum..u can find them..

24
eureka123 ·

here is the link for 1st two
http://www.targetiit.com/iit-jee-forum/posts/area-262.html

3
msp ·

yeah it is a weird ,i remember that this type of qn was created by nishant sir.

1
Grandmaster ·

ok got the 1st....wht abt 2nd and third!!!

11
Mani Pal Singh ·

2nd and3rd
x belongs to R

1
Grandmaster ·

@manipal can u give the full solution!!!!

106
Asish Mahapatra ·

1)f(x)=limn->∞cos(n! 2Πx)
2)g(x)=limn->∞cosn( 2Πx)
3)h(x)=limn->∞{cos(nx) + 2}1/n

(1)
CASE I: x is rational
Let x=p/q where p,q is an integer
as n→∞, so n! will cancel out any possible value of q
So the expression inside cos will be cos(2mÎ ) where m is an integer
So, its value will be 1

CASE II: x is irrational
Then for no value of n! the irrational value of x can be canceled. So,
here cos() can take any value from -1 to 1 depending upon the value of x

So, domain of x = R
and range = (-1,1]

(2)

x can take any value. And the range will be [-1,1]

(3) x can take any value and range will be 1

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