a quantity whoever reference to the variable is equivalent to that a specific straight line drawn in a circle whoever distance is unity, to the length of a corresponding are regarding the group. Allow AB be an arc in a circle, whose radius OA is unity let AC be a quadrant, and let OC, DB, and AF be drawnpependicular to OA, and EB and CG parallel to OA, and allow OB be produced to G and F. E Then BD is the sine of arc AB; OD or EB is the cosine, AF could be the tangent, CG is the cotangent, OF is the secant OG is the cosecant, AD may be the versed sine, and CE could be the coversed sine associated with are AB. If period of AB be represented by x (OA being unity) then your lengths of features. these outlines (OA becoming unity) are the trigonometrical features of x, as they are written sin x, cos x, tan x (or tang x), cot x, sec x, cosec x, versin x, coversin x. These quantities may also be regarded as functions for the angle BOA.