Angles used to illustrate the sum and difference of two angles and trig identities.
Claude Irwin Palmer Library of Practical Electricity: Practical Mathematics For Home Study (New York: McGraw-Hill Book Company, Inc., 1919) 455
2400×2397, 237.9 KiB
1024×1022, 31.2 KiB
640×639, 18.4 KiB
320×319, 8.1 KiB