Let f(x)= casesx-1, & x is even,\ 2x, & x is odd, cases x . If for some a , f(f(f(a)))=21, then x - \ |x|3a- [ xa ] \, where [t] denotes the greatest integer less than or equal to t, is equal to :
- 169
- 121
- 225
- 144
Answer
(4) 144
Solution
a odd: a 2a (even) 2a-1 (odd) 4a-2 (even) 21
a even: a -1 (odd) 2a-2 (even) 2a-3=21 =12
As x 12-: x12 1- [ x12 ]=0
Limit = 12312-0=144
Answer: (4)