Question

Find the fourth proportional of $3,12$ and $4$.

Answer 1

Let $x$ be the fourth proportional

$\frac{3}{12}=\frac{4}{x}$

$\Rightarrow \frac{3}{4\times 3}=\frac{4}{x}\Rightarrow \frac{1}{4}=\frac{4}{x}$

$\Rightarrow x=4\times 4=16$

$⟹x=4$

$\Rightarrow 3,12$ & $4,16$ are in proportion.