In this section, we see how Newton's Binomial Theorem can be used to derive another useful identity. We begin by establishing a different recursive formula for $P(p,k)$ than was used in our definition of it.
Our goal in this section will be to invoke Newton's Binomial Theorem with the exponent $p=-1/2$. To do so in a meaningful manner, we need a simplified expression for $C(-1/2,k)$, which the next lemma provides.
Now recalling Proposition 8.3 about the coefficients in the product of two generating functions, we are able to deduce the following corollary of Theorem 8.12 by squaring the function $f(x) = (1-4x)^{-1/2}$.