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 Inverse Trig Functions The six functions sin-1, cos-1, tan-1, csc-1, sec-1, and cot-1. These are also written arcsin, arccos, arctan, arccsc, arcsec, and arccot.   Technical note: Since none of the six trig functions sine, cosine, tangent, cosecant, secant, and cotangent are one-to-one, their inverses are not functions. Each trig function can have its domain restricted, however, in order to make its inverse a function. Some mathematicians write these restricted trig functions and their inverses with an initial capital letter (e.g. Cos or Cos-1). However, most mathematicians do not follow this practice. This website does not distinguish between capitalized and uncapitalized trig functions.     See also Inverse trigonometry