Let [t] denote the largest integer less than or equal to t. If 03 ( [x2 ] + [ x22 ] )dx = a + b 2 - 3 - 5 + c 6 - 7, where a, b, c Z, then a + b + c is equal to .
Answer
23
Solution
[x2 ] rises by 1 at each x = k (k = 1, 2, , 8); each rise adds a strip of area 1 (3 - k )
03 [x2 ]dx = k=18 (3 - k )
= 24 - (1 + 2 + 3 + 2 + 5 + 6 + 7 + 2 2 )
= 21 - 3 2 - 3 - 5 - 6 - 7
[ x22 ] rises by 1 at x = 2, 2, 6, 8:
03 [ x22 ]dx = 12 - ( 2 + 2 + 6 + 2 2 ) = 10 - 3 2 - 6
Sum = 31 - 6 2 - 3 - 5 - 2 6 - 7
a = 31, b = -6, c = -2 a + b + c = 23
Answer: 23