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

Explanation

To determine which of the given functions are strictly decreasing on the interval \([0, \frac{\pi}{2}]\), we will analyze each function by finding its derivative and checking the sign of the derivative over the specified interval.

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

1. **Find the derivative**:
\[ f'(x) = -\sin x \]
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