Let [ ] denote the greatest integer function. If the domain of the function f(x)= -1 ( x+[x]3 ) is [ , ), then 2+ 2 is equal to :
- 2
- 5
- 10
- 13
Answer
(2) 5
Solution
-1t is defined only for -1 t 1, so
-1 x + [x]3 1 -3 x + [x] 3
Let x [n, n + 1), n Z; then [x] = n and x + [x] [2n, 2n + 1).
For n = -2, x + [x] [-4, -3), every value is <-3, so it is rejected.
For n = -1, 0, 1 the ranges are [-2, -1), [0, 1) and [2, 3), all allowed.
For n = 2, x + [x] [4, 5), every value is >3, so it is rejected.
Hence the domain is [-1, 0) [0, 1) [1, 2) = [-1, 2), so = -1, = 2.
2 + 2 = 1 + 4 = 5
Answer: (2)