Find the value(s) of a for which `f(x)=x^3-a x` is an increasing function on `R` .

Explanation

To determine the values of \( a \) for which the function \( f(x) = x^3 - ax \) is an increasing function on \( \mathbb{R} \), we need to follow these steps:

### Step 1: Find the derivative of the function
We start by finding the first derivative of the function \( f(x) \):
\[ f'(x) = \frac{d}{dx}(x^3 - ax) = 3x^2 - a \]

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