square roots

• How to Convert Radicals to Decimals Without a Calculator
  Estimate a radical without a calculator by bracketing it between perfect powers, testing decimal candidates, or using the square-root long-division method.
• How Do You Find the Square Root of a Negative Number?
  A negative real number has no real square root. In the complex numbers, its principal square root is i times the square root of its positive opposite.
• Why Can’t a Negative Number Have a Real Square Root?
  No real number squares to a negative value, but complex numbers provide square roots: for a > 0, the roots of −a are ±i√a.