Negative Cotangent Angles
Illustration that can be used to show that if the cotangent of an angle is negative the angle must terminate in either the second or fourth quadrant.
George N. Bauer, PH.D. and W.E. Brooke, C.E., M.A. Plane And Spherical Trigonometry (Boston: D.C. Heath & Co., 1917) 80
Courtesy the private collection of Roy Winkelman