Returns a BigNumber whose value is the square root of the value of this BigNumber, rounded according to the current DECIMAL_PLACES and ROUNDING_MODE settings.

The return value will be correctly rounded, i.e. rounded as if the result was first calculated to an infinite number of correct digits before rounding.

x = new BigNumber(16)
x.squareRoot()                  // '4'
y = new BigNumber(3)
y.squareRoot()                  // '1.73205080756887729353'