Chapter 4: Problem 1
Use the properties of the gamma function to evaluate the following: a. \(\Gamma(6)\) b. \(\Gamma(5 / 2)\) c. \(\Gamma(9 / 2)\)
Short Answer
Expert verified
\( \Gamma(6) = 120 \), \( \Gamma(5/2) = \frac{3\sqrt{\pi}}{4} \), \( \Gamma(9/2) = \frac{105\sqrt{\pi}}{16} \).
Step by step solution
01
Understanding the Gamma Function
The gamma function, denoted as \( \Gamma(n) \), is a generalization of the factorial function for complex and real number arguments. It is defined as \( \Gamma(n) = (n-1)! \) when \( n \) is a positive integer. For non-integer values, it satisfies the recursive property \( \Gamma(n+1) = n \cdot \Gamma(n) \). Additionally, \( \Gamma(1/2) = \sqrt{\pi} \). These properties will be used to evaluate the given expressions.
02
Evaluate \( \Gamma(6) \)
Since 6 is an integer, we can directly use the factorial property of the gamma function. Thus, \( \Gamma(6) = (6-1)! = 5! \). Calculating 5!, we multiply all positive integers up to 5: \( 5! = 5 \times 4 \times 3 \times 2 \times 1 = 120 \). Therefore, \( \Gamma(6) = 120 \).
03
Evaluate \( \Gamma(5/2) \) Using Recursion
To find \( \Gamma(5/2) \), we use the recursive property \( \Gamma(n+1) = n \cdot \Gamma(n) \). First, relate \( \Gamma(5/2) \) to \( \Gamma(3/2) \): \( \Gamma(5/2) = \frac{3}{2} \cdot \Gamma(3/2) \). Now, use \( \Gamma(3/2) = \frac{1}{2} \cdot \Gamma(1/2) \) and since \( \Gamma(1/2) = \sqrt{\pi} \), \( \Gamma(3/2) = \frac{1}{2} \times \sqrt{\pi} = \frac{\sqrt{\pi}}{2} \). Plug this into the previous equation: \( \Gamma(5/2) = \frac{3}{2} \times \frac{\sqrt{\pi}}{2} = \frac{3\sqrt{\pi}}{4} \).
04
Evaluate \( \Gamma(9/2) \) Using Recursion
Finding \( \Gamma(9/2) \) also involves recursion. Start with \( \Gamma(9/2) = \frac{7}{2} \cdot \Gamma(7/2) \). Calculate \( \Gamma(7/2) = \frac{5}{2} \cdot \Gamma(5/2) \) where \( \Gamma(5/2) = \frac{3 \sqrt{\pi}}{4} \) from Step 3. Thus, \( \Gamma(7/2) = \frac{5}{2} \times \frac{3 \sqrt{\pi}}{4} = \frac{15 \sqrt{\pi}}{8} \). Now find \( \Gamma(9/2) = \frac{7}{2} \times \frac{15 \sqrt{\pi}}{8} = \frac{105 \sqrt{\pi}}{16} \). The answer for \( \Gamma(9/2) \) is \( \frac{105 \sqrt{\pi}}{16} \).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Factorial Function
The factorial function is a surprisingly crucial concept in mathematics. Its most familiar use is the expression of ":n!" pronounced as "n factorial." If you see a number followed by an exclamation point, this tells you to multiply all positive integers up to that number. So,
- For example, 5! = 5 × 4 × 3 × 2 × 1 = 120.
- \( \Gamma(n) = (n-1)! \) for integer \( n \).
Recursive Property
The recursive property of the gamma function is a powerful tool for calculations, especially when working outside the realm of integers. It essentially states:
- \( \Gamma(n+1) = n \cdot \Gamma(n) \).
Non-integer Arguments
One of the most intriguing aspects of the gamma function is how it accommodates non-integer arguments, which the factorial function alone cannot handle. While factorials are confined to whole numbers, the gamma function provides a way to "extend" this concept to values such as fractions or even complex numbers.This versatility is evident in evaluations like \( \Gamma(5/2) \). Instead of performing what seems an impossible task—calculating a fraction of a factorial—the gamma function manages it through its recursive relationships. Each step builds on the last, effectively computing the value by navigating orderly through calculations.
- For instance, using \( \Gamma\left(\frac{1}{2}\right) = \sqrt{\pi} \), allows a direct entry point to calculate related gamma values involving half-integer multiples.