it's a cube-root instead of a square-root
when you write the square-root sign, it is implied that there is a 2 there, so they never put it, but when you have a root that is anything over than 2, they put the number there, such as a cube-root, or a forth-root
so what a square root means is "what number multiplied by itself once (X times X) will give me the number i have"
ex square root of 4, what number multiplied by itself gives me 4, so 2 is the square root of 4
so if i have a cube root, i say "what number multiplied by itself twice (X times X times X) will give me the number i have"
ex cube root of 8, what number [X times X times X] gives me 8? i've chosen this example to be easy again, 2 times 2 times 2 = 8, so the cube root of 8 is 2
there is a way to calculate this on any fancy calculator, you'll see the root button with a x where the 3 is, again if the root is 2, then they just leave it out of the symbol