JEE Main202126 Feb 2021Evening ShiftMathematicsFunctionsActual
Let A = 1 , 2 , 3 , … , 10 and f : A → A be defined as f k = k + 1 if k is odd k if k is even Then the number of possible functions g : A → A such that g o f = f is:
Options
- AC 5 10
- B5 5
- C5 !
- D10 5
Correct answer
D. 10 5
Step-by-step solution
f x = x + 1 if   x   is odd x if   x   is even ∵   g : A → A such that g f x = f x ⇒ If x is even then g x = x       … 1 If x is odd then g x + 1 = x + 1       … 2 from 1 and 2 we can say that g x = x if x is even ⇒ If x is odd then g x can take any value in set A so number of g x = 10 5 × 1