- Data Structure
- Networking
- RDBMS
- Operating System
- Java
- MS Excel
- iOS
- HTML
- CSS
- Android
- Python
- C Programming
- C++
- C#
- MongoDB
- MySQL
- Javascript
- PHP
- Physics
- Chemistry
- Biology
- Mathematics
- English
- Economics
- Psychology
- Social Studies
- Fashion Studies
- Legal Studies
- Selected Reading
- UPSC IAS Exams Notes
- Developer's Best Practices
- Questions and Answers
- Effective Resume Writing
- HR Interview Questions
- Computer Glossary
- Who is Who
Why negative multiplied by negative is positive?
Solution :
Let a and b be any two real numbers.
Consider the number x defined by
$x = ab + (-a)(b) + (-a)(-b)$.
We can write
$x = ab + (-a)[ (b) + (-b) ]$
$= ab + (-a)(0)$
$= ab + 0$
$= ab$.
Also,
$x = [ a + (-a) ]b + (-a)(-b)$
$= 0 \times b + (-a)(-b)$
$= 0 + (-a)(-b)$
$= (-a)(-b)$.
So we have $x = ab$ and $x = (-a)(-b)$
Therefore, $ab = (-a) (-b)$
Hence, negative times negative is positive.
Advertisements