Answer:
[tex]-\frac{3+\sqrt{5}}{4}[/tex]
Step-by-step explanation:
[tex]\sqrt{20} \leq 5 \implies f(\sqrt{20})=\frac{2}{\sqrt{20}-6} \\ \\ =\frac{1}{\sqrt{5}-3} \\ \\ =\frac{\sqrt{5}+3}{-4} \\ \\ =-\frac{3+\sqrt{5}}{4}[/tex]
