Find the values of x such that
`f(x)=2x^(3)-15x^(2)-84x-7` is a decreasing function.

Explanation

To determine the values of \( x \) for which the function \( f(x) = 2x^3 - 15x^2 - 84x - 7 \) is decreasing, we need to follow these steps:

### Step 1: Find the derivative of \( f(x) \)
To find where the function is decreasing, we first find the derivative \( f'(x) \).

\[ f'(x) = \frac{d}{dx}(2x^3 - 15x^2 - 84x - 7) \]
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