Euler is the most prolific outstanding mathematician in the history of science. According to statistics, * * * has written 886 books and papers in his tireless life, of which 40% is analysis, algebra and number theory, 18% is geometry, 28% is physics and mechanics, 1 1% is astronomy, as well as ballistics and navigation. /kloc-Gauss (1777- 1855), a great mathematician in the 9th century, once said: "Studying Euler's works is always the best way to understand mathematics."
Modern trigonometry began with Euler's introduction to infinite analysis. He defined the unit circle and trigonometric function by the ratio of function line to radius. He also created lowercase Latin letters A, B and C to represent the three sides of a triangle, and uppercase Latin letters A, B and C to represent the three angles of a triangle, thus simplifying the triangle formula, and further transforming trigonometry from studying triangle solutions to studying trigonometric functions and their applications, becoming a relatively complete branch of mathematics.