Find the simplest rationalising factor
\[ \sqrt{3} + \sqrt{5} \]
Solution:
\[ \text{Rationalising factor of } (a + b) = (a – b) \]
\[ \therefore \text{Rationalising factor of } (\sqrt{3} + \sqrt{5}) = \sqrt{3} – \sqrt{5} \]
\[ (\sqrt{3} + \sqrt{5})(\sqrt{3} – \sqrt{5}) = 3 – 5 = -2 \ (\text{rational}) \]
\[ \therefore \text{Correct Answer: } \sqrt{3} – \sqrt{5} \ (\text{Option c}) \]