Write a function in python to evaluate the Chebyshev polynomials using only core Python and the "math" module (ie. don't just call a library function for this task).

Your function should be defined so that it can be called as follows:

y = Chebyshev1_recur(x, n)

In other words, if the degree n and a single value x are provided, then a single value equal to Tn(x) should be returned.