S'anomena arrel n-èsima del nombre x, el nombre y que elevat a n dona x:      «math xmlns=¨http://www.w3.org/1998/Math/MathML¨»«mroot mathcolor=¨#003300¨»«mi mathvariant=¨bold¨»x«/mi»«mi mathvariant=¨bold¨»n«/mi»«/mroot»«mo mathvariant=¨bold¨ mathcolor=¨#003300¨»=«/mo»«mi mathvariant=¨bold¨ mathcolor=¨#003300¨»y«/mi»«mo mathvariant=¨bold¨ mathcolor=¨#003300¨»§#160;«/mo»«mo mathvariant=¨bold¨ mathcolor=¨#003300¨»§#8660;«/mo»«msup mathcolor=¨#003300¨»«mi mathvariant=¨bold¨ mathcolor=¨#003300¨»y«/mi»«mrow»«mi mathvariant=¨bold¨»n«/mi»«mo mathvariant=¨bold¨»§#160;«/mo»«/mrow»«/msup»«mo mathvariant=¨bold¨ mathcolor=¨#003300¨»=«/mo»«mo mathvariant=¨bold¨ mathcolor=¨#003300¨»§#160;«/mo»«mi mathvariant=¨bold¨ mathcolor=¨#003300¨»x«/mi»«/math»

També es pot escriure com un exponent FRACCIONARI:

«math xmlns=¨http://www.w3.org/1998/Math/MathML¨»«mroot mathcolor=¨#003300¨»«msup»«mi mathvariant=¨bold¨»x«/mi»«mi mathvariant=¨bold¨»m«/mi»«/msup»«mi mathvariant=¨bold¨»n«/mi»«/mroot»«mo mathvariant=¨bold¨ mathcolor=¨#003300¨»=«/mo»«msup mathcolor=¨#003300¨»«mi mathvariant=¨bold¨ mathcolor=¨#003300¨»x«/mi»«mfrac»«mi mathvariant=¨bold¨»m«/mi»«mi mathvariant=¨bold¨»n«/mi»«/mfrac»«/msup»«/math»