More generally: when 0≤k≤n, the binomial coefficient (n choose k) is equal to the coefficient of x^k in the polynomial (1 x)^n.
For k,n arbitrary integers with k≥0, one should extend this by defining (n choose k) to be the coefficient of x^k in the formal power series (1 x)^n
I’ve made an important mathematical discovery; apparently -1 choose 0 is equal to 1, since there’s one way to put zero indistinguishable items in zero bins