There are several q-analogs of the cosine function. The two natural definitions of the q-cosine defined by Koekoek and Swarttouw are given by cos_q(z) | = | sum_(n = 0)^∞ ((-1)^n z^(2n))/(q;q)_(2n) | = | (e_q(i z) + e_q(-i z))/2 Cos_q(z) | = | (E_q(i z) + E_q(-i z))/2, where e_q(z) and E_q(z) are q-exponential functions.

q-exponential function | q-factorial | q-pi | q-sine