In the recent update of the app, we have included the handling of complex numbers. From now on, if you calculate sqrt(-1), the result is i. All the functions handle complex numbers so cos(i) works as well. Complex numbers are useful in a wide variety of engineering calculations and also in many scientific problems.
We haven’t yet included Gaussian integers so number theoretic functions, such as gcd, still work only with integers. We are going to add them in a future release.