# Theory of Equation (Descarte's Rule of Sign)

Most of the people I see gets confused about this rule. This rule actually cannot determine the number of roots. Specifically, this rule determines the NUMBER OF MAXIMUM real positive or negative roots by checking the number of change of signs in f(x) and f(-x). The word MAXIMUM should be given emphasis.

For the people who don't know this rule: Check this link http://en.wikipedia.org/wiki/Descartes'ruleof_signs

Note by Saswata Dasgupta
5 years, 6 months ago

This discussion board is a place to discuss our Daily Challenges and the math and science related to those challenges. Explanations are more than just a solution — they should explain the steps and thinking strategies that you used to obtain the solution. Comments should further the discussion of math and science.

When posting on Brilliant:

• Use the emojis to react to an explanation, whether you're congratulating a job well done , or just really confused .
• Ask specific questions about the challenge or the steps in somebody's explanation. Well-posed questions can add a lot to the discussion, but posting "I don't understand!" doesn't help anyone.
• Try to contribute something new to the discussion, whether it is an extension, generalization or other idea related to the challenge.

MarkdownAppears as
*italics* or _italics_ italics
**bold** or __bold__ bold
- bulleted- list
• bulleted
• list
1. numbered2. list
1. numbered
2. list
Note: you must add a full line of space before and after lists for them to show up correctly
paragraph 1paragraph 2

paragraph 1

paragraph 2

[example link](https://brilliant.org)example link
> This is a quote
This is a quote
    # I indented these lines
# 4 spaces, and now they show
# up as a code block.

print "hello world"
# I indented these lines
# 4 spaces, and now they show
# up as a code block.

print "hello world"
MathAppears as
Remember to wrap math in $$ ... $$ or $ ... $ to ensure proper formatting.
2 \times 3 $2 \times 3$
2^{34} $2^{34}$
a_{i-1} $a_{i-1}$
\frac{2}{3} $\frac{2}{3}$
\sqrt{2} $\sqrt{2}$
\sum_{i=1}^3 $\sum_{i=1}^3$
\sin \theta $\sin \theta$
\boxed{123} $\boxed{123}$

Sort by:

I think this rule also tells us about the complex roots.

- 5 years, 6 months ago

Obviously you can get the MAXIMUM number of complex roots by taking out the number of MAXIMUM real roots from the total roots

- 5 years, 6 months ago

Yes I've checked the wolfram. It also says this.

- 5 years, 6 months ago

Can you contribute to the wiki on Descartes Rule of Sign here on Brilliant ?

Thanks :)

- 5 years, 6 months ago

Sure, but can you tell me how can I contribute?

- 5 years, 6 months ago

It's simple really !

Just got to the link that I have provided, click on "edit this page" and add the content that you think is appropriate :)

- 5 years, 6 months ago