Find the value of
(i) cos 15 `pi` (ii) sin 16`pi` (iii) cos `(-pi)`
(iv) sin 5`pi` (v) tan `((5pi)/(4))` (vi) sec 6`pi`

Explanation

To find the values of the trigonometric functions given in the question, we will use the properties of sine and cosine functions, particularly their periodicity and symmetry.

### Step-by-Step Solution:

1. **Finding \( \cos(15\pi) \)**:
- The cosine function has a period of \( 2\pi \). Thus, we can reduce \( 15\pi \) modulo \( 2\pi \):
\[
15\pi \mod 2\pi = 15\pi - 7(2\pi) = 15\pi - 14\pi = \pi
...