Editing Angle (section)

===Hyperbolic angle===
A [[hyperbolic angle]] is an [[argument of a function|argument]] of a [[hyperbolic function]] just as the ''circular angle'' is the argument of a [[circular function]]. The comparison can be visualized as the size of the openings of a [[hyperbolic sector]] and a [[circular sector]] since the [[area]]s of these sectors correspond to the angle magnitudes in each case.<ref>[[Robert Baldwin Hayward]] (1892) [https://archive.org/details/algebraofcoplana00haywiala/page/n5/mode/2up ''The Algebra of Coplanar Vectors and Trigonometry''], chapter six</ref> Unlike the circular angle, the hyperbolic angle is unbounded. When the circular and hyperbolic functions are viewed as [[infinite series]] in their angle argument, the circular ones are just [[alternating series]] forms of the hyperbolic functions. This comparison of the two series corresponding to functions of angles was described by [[Leonhard Euler]] in ''[[Introduction to the Analysis of the Infinite]]'' (1748).