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Question: Answered & Verified by Expert
Let N be the set of natural numbers and two functions f and g be defined as f,g:NN such that

fn=n+12,   if n is odd   n2,    if n is even

and gn=n--1n. Then fog is:
MathematicsFunctionsJEE MainJEE Main 2019 (10 Jan Shift 2)
Options:
  • A onto but not one-one
  • B Both one-one and onto
  • C One-one but not onto
  • D Neither one-one nor onto
Solution:
1691 Upvotes Verified Answer
The correct answer is: onto but not one-one
We have, gn=n+1, ifnoddn-1, ifneven

fg1=f(2)=1

fg2=f(1)=1

fgx is many one.

fg2k=f(2k-1)=k

fg2k+1=f2k+2=k+1

f(g(x)) is onto.

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