https://docs.oracle.com/cd/E88353_01/html/E37846/csqrt-3m.html
csqrt - man pages section 3: Extended Library Functions, Volume 2
csqrt , csqrtf , csqrtl - complex square root functions These functions compute the complex square root of z , with a branch cut along the negative real axis.
man pagesextended librarycsqrtsectionfunctions