Determine the antiderivative of $f(x)=x$.

Since $f(x)=x=x^1$, we can use Antiderivative Rule 4 to find that
$$\begin{eqnarray} F(x)&=&\frac{1}{1+1}x^{1+1}\\ &=&\frac{1}{2}x^2. \end{eqnarray}$$