# Q-cos sub q

(Redirected from Q-cos)
The function $\cos_q$ is defined for $|z|<1$ by $$\cos_q(z)=\dfrac{e_q(iz)+e_q(-iz)}{2},$$ where $e_q$ denotes the $q$-exponential $e$ and $(q;q)_{2k}$ denotes the $q$-Pochhammer symbol.