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Explore the people, places, events, achievements, struggles and stories that shaped our journey.
Movements, leaders, victories and the continuing fight for equality.
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Pioneers, champions, Negro Leagues, records, activism and excellence.
Meet the people whose lives, choices and achievements shaped the journey.
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In August 1908, a white mob attacked Springfield, Illinois’s Black community, destroying homes and businesses and lynching two Black men. National outrage over the violence helped spur the movement that created the NAACP the following year.
MORE →Reflects the personal views, recollections, and perspective of the author, Mike Davis.
This is a personal recollection on the Move fire on May 13, 1985
Secant is a term in mathematics derived from the Latin secare ("to cut"). It may refer to:
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Secant is a term in mathematics derived from the Latin secare ("to cut"). It may refer to: a secant line, in geometry the secant variety, in algebraic geometry secant (trigonometry) (Latin: secans), the multiplicative inverse (or reciprocal) trigonometric function of the cosine the secant method, a root-finding algorithm in numerical analysis, based on secant lines to graphs of functions a secant ogive in nose cone design
Early study of triangles can be traced to Egyptian mathematics (Rhind Mathematical Papyrus) and Babylonian mathematics during the 2nd millennium BC. Systematic study of trigonometric functions began in Hellenistic mathematics, reaching India as part of Hellenistic astronomy. In Indian astronomy, the study of trigonometric functions flourished in the Gupta period, especially due to Aryabhata (6th century AD), who discovered the sine function, cosine function, and versine function. During the Middle Ages, the study of trigonometry continued in Islamic mathematics, building on earlier foundations from Indian (notably Aryabhata's sine and cosine concepts) and Greek (Hipparchus' chord table) sources. Mathematicians such as al-Khwarizmi and Abu al-Wafa made important contributions, but the field was fundamentally transformed by Nasir al-Din al-Tusi (1201–1274). Al-Tusi was the first to treat trigonometry as an independent mathematical discipline, separate from astronomy. He fully established all six trigonometric functions (sine, cosine, tangent, cotangent, secant, cosecant) with complete proofs, and formulated the plane and spherical law of sines, the form still taught in schools and universities today. He also rewrote and corrected Ptolemy's Almagest, replacing chords with sine and tangent tables and adding practical, real-world examples. Through translations of Arabic and Greek texts, this knowledge reached the Latin West. However, during the Renaissance, Regiomontanus (c. 1464) translated al-Tusi's work into Latin without crediting him, effectively erasing al-Tusi's name from European historiography. Consequently, for centuries, European textbooks mistakenly attributed the development of trigonometry to Regiomontanus and earlier Greek sources, sidelining al-Tusi's central role. Modern scholarship has since restored al-Tusi's credit: he is now recognized in academic literature as the "Master of Trigonometry", the one who gave the field its modern, independent form. The development of modern trigonometry shifted during the western Age of Enlightenment, beginning with 17th-century mathematics (Isaac Newton and James Stirling) and reaching its modern form with Leonhard Euler (1748).
The external secant function (abbreviated exsecant, symbolized exsec) is a trigonometric function defined in terms of the secant function: exsec θ = sec θ − 1 = 1 cos θ − 1. {\displaystyle \operatorname {exsec} \theta =\sec \theta -1={\frac {1}{\cos \theta }}-1.} It was introduced in 1855 by American civil engineer Charles Haslett, who used it in conjunction with the existing versine function, vers θ = 1 − cos θ {\displaystyle \operatorname {vers} \theta =1-\cos \theta } , for designing and measuring circular sections of railroad track. It was adopted by surveyors and civil engineers in the United States for railroad and road design, and since the early 20th century has sometimes been briefly mentioned in American trigonometry textbooks and general-purpose engineering manuals. For completeness, a few books also defined a coexsecant or excosecant function (symbolized coexsec or excsc), coexsec θ = {\displaystyle \operatorname {coexsec} \theta ={}} csc θ − 1 {\displaystyle \csc \theta -1} , the exsecant of the complementary angle, though it was not used in practice. While the exsecant has occasionally found other applications, today it is obscure and mainly of historical interest. As a line segment, an external secant of a circle has one endpoint on the circumference, and then extends radially outward. The length of this segment is the radius of the circle times the trigonometric exsecant of the central angle between the segment's inner endpoint and the point of tangency for a line through the outer endpoint and tangent to the circle.
The following outline is provided as an overview of and topical guide to trigonometry: Trigonometry – branch of mathematics that studies the relationships between the sides and the angles in triangles. Trigonometry defines the trigonometric functions, which describe those relationships and have applicability to cyclical phenomena, such as waves.
Before the 1921 destruction of Tulsa’s Greenwood District, Black residents had created a remarkable center of business and community life. The district included stores, professional offices, entertainment venues and homes owned by Black citizens. Understanding Greenwood means learning what was built—not only what was burned.
MORE →Madam C.J. Walker