Let [.] denote the greatest integer function. If 0e3 [ 1ex-1 ] dx = - e 2, then 3 is equal to .
Answer
8
Solution
1ex-1 = e1-x decreases from e (at x = 0) and equals 1 at x = 1.
[e1-x] = 2 when e1-x 2 x 1 - e 2
[e1-x] = 1 when 1 - e 2 < x 1
[e1-x] = 0 when x > 1 (up to e3)
Integral = 2(1 - e 2) + 1 e 2 + 0 = 2 - e 2
= 2 3 = 8
Answer: 8