[tex]\dfrac{12}{\sqrt 2} + \sqrt{18}\\\\\\=\dfrac{12 + \sqrt{18 \times 2}}{\sqrt 2}\\\\\\=\dfrac{12+\sqrt{9 \times 4}}{\sqrt 2}\\\\\\=\dfrac{12+3 \times 2}{\sqrt 2}\\\\\\=\dfrac{18}{\sqrt 2}\\\\\\=\dfrac{18\sqrt 2}{\left(\sqrt 2\right)^2}\\\\\\=\dfrac{18\sqrt 2}2\\\\\\=9\sqrt 2[/tex]
