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 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