Let [t] denote the greatest integer less than or equal to t. Let f : [0, ) R be a function defined by f(x) = [ x2 + 3 ] - [ x]. Let S be the set of all points in the interval [0, 8] at which f is not continuous. Then a S a is equal to .
Answer
17
Solution
f(x) = [ x2 ] + 3 - [ x] ( [t + 3] = [t] + 3 )
[ x2 ] jumps up by 1 at x = 2, 4, 6, 8; [ x] jumps up by 1 at x = 1, 4
At x = 4 both jumps cancel:
f(4-) = 1 + 3 - 1 = 3, f(4) = 2 + 3 - 2 = 3 continuous
At x = 0 (left end of the domain): f = 3 on [0, 1) continuous
At x = 1, 2, 6, 8 only one part jumps discontinuous
S = \1, 2, 6, 8\
a S a = 1 + 2 + 6 + 8 = 17
Answer: 17