118 - 32=12×3×3 - 2×2×2×2×2=132 - 42=1-2=-12 × 22=-22

Maths

\frac{1}{\sqrt{18} - \sqrt{32}} = \frac{1}{\sqrt{2 \times 3 \times 3} - \sqrt{2 \times 2 \times 2 \times 2 \times 2}} = \frac{1}{3 \sqrt{2} - 4 \sqrt{2}} = \frac{1}{- \sqrt{2}} = - \frac{1}{\sqrt{2}} \times \frac{\sqrt{2}}{\sqrt{2}} = - \frac{\sqrt{2}}{2}