13) \( -\sqrt{6}+2 \sqrt{6}-\sqrt{18} \)

To simplify the expression, start by combining like terms. You have \( -\sqrt{6} + 2\sqrt{6} \), which simplifies to \( \sqrt{6} \). Next, simplify \( \sqrt{18} \). Since \( \sqrt{18} = \sqrt{9 \times 2} = 3\sqrt{2} \), the expression becomes \( \sqrt{6} - 3\sqrt{2} \). Therefore, the final result is \( \sqrt{6} - 3\sqrt{2} \). Isn't it fascinating how math allows us to strip away complexity and reveal elegant results? You can think of simplifying radical expressions as a treasure hunt—searching for like terms and simplifying radicals is like digging for gems hidden beneath layers of dirt!