The 4th root of 2 to the 4th power is 2.
We use the laws of exponents to calculate nth roots.
Older kanji spelling using 冪 (べき, 'power'), now largely replaced by べき根.
Compound of べき (power) and 根 (root). The kanji 冪 is an older character for 'power' that has been largely replaced by kana in modern usage.