Solution for Section 3.5 Question 5

5. Suppose that n is an odd integer. We need to show that lceil.jpg (551 bytes)n / 2rceil.jpg (532 bytes) = lfloor.jpg (533 bytes)n / 2rfloor.jpg (530 bytes)+ 1.

Proof Since n is an odd integer, n = 2k + 1   for some integer k. 

Left-hand side: lceil.jpg (551 bytes)n / 2rceil.jpg (532 bytes) = lceil.jpg (551 bytes)(2k + 1) / 2rceil.jpg (532 bytes) = lceil.jpg (551 bytes)k + 1/2rceil.jpg (532 bytes) = k + 1 (by the definition of ceiling, see illustration below).
Right-hand side: lfloor.jpg (533 bytes) n / 2 rfloor.jpg (530 bytes)+ 1 = lfloor.jpg (533 bytes) (2k + 1) / 2 rfloor.jpg (530 bytes)+ 1 = lfloor.jpg (533 bytes)k + 1/2rfloor.jpg (530 bytes)+ 1 = k + 1  (by the definition of floor, see illustration below).

numline.jpg (2226 bytes)

Thus lceil.jpg (551 bytes)n / 2rceil.jpg (532 bytes) = lfloor.jpg (533 bytes)n / 2rfloor.jpg (530 bytes)+ 1.

Back to Section 3.5