Triangle in Quadrant I Small 320×315 Medium 640×631 Large 1024×1009 Download Tiff Original 2400×2365 | (242.3 KB) Description Illustration of an angle &alpha with the terminal side used to draw a triangle in quadrant I. Keywords acute, angle, cos, cosine, quadrant 1, reference, sin, Sine, Tan, tangent, triangles, trig functions, trigonometric, trigonometry Galleries Trigonometry: Triangles Source: George N. Bauer, PH.D. and W.E. Brooke, C.E., M.A. Plane And Spherical Trigonometry (Boston: D.C. Heath & Co., 1917) 113 Courtesy the private collection of Roy Winkelman