Question

Find the third proportional to 9 and 6.

Answer 1

If $$x$$ is the third proportional to $$a$$ and $$b$$, then $$a : b :: b : x \Rightarrow x = \frac{b^2}{a}$$.

$$x = \frac{6^2}{9} = \frac{36}{9} = 4$$