Derivatives of symmetric expressions

In summary, the conversation discusses the clean expression for $f'(x)$ and $f''(x)$ for two different functions involving a product of fractions. The speaker suggests using the relation $\frac{d}{dx} \ln f(x) = \frac{f'(x)}{f(x)}$ and provides a formula for $f'(x)$ using this relation. They also mention that the same procedure can be used for the second function.
  • #1
kalish1
99
0
So I was bored in math class and came up with this series of related questions, that I cannot answer:

Is there a clean expression for $f'(x),$ where $$f(x)=\prod_{i=1}^{n}\dfrac{(x-i)}{(x+i)}?$$

What about for $f''(x)?$ Or for $$f(x)=\prod_{i=1}^{n}\dfrac{(x^2-i)}{(x^2+i)}?$$
 
Mathematics news on Phys.org
  • #2
kalish said:
So I was bored in math class and came up with this series of related questions, that I cannot answer:

Is there a clean expression for $f'(x),$ where $$f(x)=\prod_{i=1}^{n}\dfrac{(x-i)}{(x+i)}?$$

What about for $f''(x)?$ Or for $$f(x)=\prod_{i=1}^{n}\dfrac{(x^2-i)}{(x^2+i)}?$$

You can use the relation...

$\displaystyle \frac{d}{d x} \ln f(x) = \frac{f^{\ '} (x)}{f(x)} \implies f^{\ '} (x) = f(x)\ \frac{d}{d x} \ln f(x)\ (1)$

... and in this case...

$\displaystyle \frac{d}{d x} \ln f(x) = \sum_{i = 1}^{n} (\frac{1}{x - i} - \frac{1}{x + i}) = 2\ \sum_{i=1}^{n} \frac{i}{x^{2} - i^{2}}\ (2)$

The same procedure is valid also for the second function...

Kind regards

$\chi$ $\sigma$
 

Related to Derivatives of symmetric expressions

1. What are derivatives of symmetric expressions?

Derivatives of symmetric expressions are mathematical expressions that represent the rate of change of a symmetric function. They are used to find the slope or gradient of a curve at a specific point.

2. How do you find the derivative of a symmetric expression?

To find the derivative of a symmetric expression, you need to use the power rule, product rule, quotient rule, or chain rule, depending on the form of the expression. These rules involve taking the derivative of each term in the expression and combining them using algebraic operations.

3. What is the difference between derivatives of symmetric expressions and derivatives of non-symmetric expressions?

The main difference between the two is that derivatives of symmetric expressions are always equal to the derivative of the original function, while derivatives of non-symmetric expressions may not always be equal to the derivative of the original function. This is because symmetric expressions have a special property known as even or odd symmetry, which allows for simplification in the derivative calculation.

4. What are some real-life applications of derivatives of symmetric expressions?

Derivatives of symmetric expressions have many real-life applications, such as in physics, economics, and engineering. They are used to model and analyze the behavior of natural phenomena, such as motion, growth, and decay. They are also used to optimize processes and systems, such as in minimizing costs or maximizing profits.

5. Can derivatives of symmetric expressions have multiple solutions?

No, derivatives of symmetric expressions have a unique solution for a given point. This is because the derivative of a symmetric function is always an even function, meaning it is symmetric about the y-axis. Therefore, the slope at a specific point on the function will always be the same, regardless of the direction in which the point is approached.

Similar threads

Replies
3
Views
928
Replies
3
Views
396
Replies
2
Views
430
  • General Math
Replies
3
Views
846
  • General Math
Replies
3
Views
1K
  • General Math
Replies
2
Views
871
Replies
3
Views
821
Replies
5
Views
885
Replies
3
Views
1K
Back
Top