Calculate $\sqrt{x^{2}+7}$ to the power of $2$ and get $x^{2}+7$.
$$\frac{\mathrm{d}}{\mathrm{d}x}(x^{2}+7)$$
The derivative of a polynomial is the sum of the derivatives of its terms. The derivative of a constant term is $0$. The derivative of $ax^{n}$ is $nax^{n-1}$.
