cbrt, sqrt - cube root, square root
Cbrt(x) returns the cube root of x.
Sqrt(x) returns the square root of x.
Sqrt(negative) returns a NaN.
ERROR (due to Roundoff etc.)
Cbrt is accurate to within 0.7 ulps.
Sqrt on a machine that conforms to IEEE 754 is correctly rounded in
accordance with the rounding mode in force; the error is less than
half an ulp in the default mode (round-to-nearest). An ulp is one
Unit in the Last Place carried.