Power of One plus x in terms of Gaussian Hypergeometric Function
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Theorem
- $\map F {-p, 1; 1; -x} = \paren {1 + x}^p$
where:
- $x$ and $p$ are real numbers with $\size x < 1$
- $F$ denotes the Gaussian hypergeometric function.
Proof
\(\ds \map F {-p, 1; 1; -x}\) | \(=\) | \(\ds \sum_{n \mathop = 0}^\infty \frac {\paren {-p}^{\overline n} 1^{\overline n} } {1^{\overline n} } \frac {\paren {-x}^n} {n!}\) | Definition of Gaussian Hypergeometric Function | |||||||||||
\(\ds \) | \(=\) | \(\ds \sum_{n \mathop = 0}^\infty \paren {-1}^n \paren {\prod_{j \mathop = 0}^{n - 1} \paren {-p + j} } \frac {x^n} {n!}\) | Definition of Rising Factorial | |||||||||||
\(\ds \) | \(=\) | \(\ds \sum_{n \mathop = 0}^\infty \paren {\prod_{j \mathop = 0}^{n - 1} \paren {-1} } \paren {\prod_{j \mathop = 0}^{n - 1} \paren {-p + j} } \frac {x^n} {n!}\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds \sum_{n \mathop = 0}^\infty \paren {\prod_{j \mathop = 0}^{n - 1} \paren {p - j} } \frac {x^n} {n!}\) | Product of Products | |||||||||||
\(\ds \) | \(=\) | \(\ds \paren {1 + x}^p\) | General Binomial Theorem |
$\blacksquare$
Sources
- 1968: Murray R. Spiegel: Mathematical Handbook of Formulas and Tables ... (previous) ... (next): $\S 31$: Hypergeometric Functions: Special Cases: $31.3$