Fourth Proportional
Fourth term in a proportion with four terms.
In the proportion with four terms [latex]\dfrac {a}{b} =\dfrac {c} {d}[/latex], the term d is the fourth proportional.
Example
[latex]\dfrac {5}{8} =\dfrac {25} {x}[/latex]
By calculating, we find that the 4th proportional, which is the value of the unknown x, is 40.