Which of the following functions are strictly decreasing on `(0,pi/2)`
(A) `cos x`
(B)`cos 2x`
(C) `cos 3x`
(D) `tan x`

Explanation

To determine which of the given functions are strictly decreasing on the interval \( (0, \frac{\pi}{2}) \), we will differentiate each function and analyze the sign of the derivative.

### Step 1: Analyze the function \( f(x) = \cos x \)

1. **Differentiate**:
\[ f'(x) = -\sin x \]
...