# Fourth Proportional

## Fourth Proportional

Fourth term in a proportion with four terms.

In the proportion with four terms $$\dfrac {a}{b} =\dfrac {c} {d}$$, the term d is the fourth proportional.

### Example

$$\dfrac {5}{8} =\dfrac {25} {x}$$

By calculating, we find that the 4th proportional, which is the value of the unknown x, is 40.