If a, b and c are numbers connected by the proportion \(\dfrac{a}{b}\) = \(\dfrac{b}{c}\), then c = \(\dfrac{b^{2}}{a}\) and c is called the third proportional.
In a proportion with three terms that are, in order, a, b and c, the third proportional is c.
Examples
- In the proportion \(\dfrac{x}{12}\) = \(\dfrac{12}{16}\), 9 is the third proportional, because x = 9.
- In the proportion \(\dfrac{12}{18}\) = \(\dfrac{18}{x}\), 27 is the third proportional, because x = 27.