Definition:Power (Algebra)/Rational Number/Historical Note

Historical Note on Rational Power
The definition:
 * $x^r = x^{p/q} = \left({\sqrt [q] x}\right)^p = \sqrt [q] {\left({x^p}\right)}$

is due to circa $1360$.

The concept of a fractional exponent was introduced by in the $17$th century.