In 1813, John Herschel introduced the notation sin⁻¹(𝑥) for the inverse sine, citing inspiration from operator power notation like dⁿf used in calculus. Lagrange had previously introduced the symbol arcsin around 1772. pic.twitter.com/0a8Ikc3nVo
— Fermat's Library (@fermatslibrary) October 28, 2020