The following procedures accept any kind of number as arguments, including complex numbers.
Return the square root of z. Of the two possible roots (positive and negative), the one with the a positive real part is returned, or if that's zero then a positive imaginary part. Thus,
(sqrt 9.0) ⇒ 3.0 (sqrt -9.0) ⇒ 0.0+3.0i (sqrt 1.0+1.0i) ⇒ 1.09868411346781+0.455089860562227i (sqrt -1.0-1.0i) ⇒ 0.455089860562227-1.09868411346781i