- 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
Which of the following numbers are cubes of rational numbers:
(i) $ \frac{27}{64} $
(ii) $ \frac{125}{128} $
(iii) $ 0.001331 $
(iv) $ 0.04 $
To find:
We have to find whether the given numbers are cubes of rational numbers.
Solution:
(i) $\frac{27}{64}=\frac{3 \times 3 \times 3}{4 \times 4 \times 4}$
$=\frac{3^3}{4^3}$
$=(\frac{3}{4})^3$
Therefore,
$\frac{27}{64}$ is a perfect cube.
(ii) $\frac{125}{128}=\frac{5 \times 5 \times 5}{2 \times 2 \times 2 \times 2 \times 2 \times 2 \times 2}$
$=\frac{(5)^{3}}{(2)^{3} \times(2)^{3} \times 2}$
We observe that,
128 is not a perfect cube.
Therefore,
$\frac{125}{128}$ is not a perfect cube.
(iii) $0.001331=\frac{1331}{1000000}$
$= \frac{11 \times 11 \times 11}{10 \times 10 \times 10 \times 10 \times 10 \times 10}$
$=(\frac{11}{10 \times 10})^{3}$
$=(\frac{11}{100})^{3}$
Therefore,
0.001331 is a perfect cube.
(iv) $0.04=\frac{4}{100}$
$= \frac{2 \times 2}{10 \times 10}$
$=(\frac{2}{10})^{2}$
Therefore,
0.04 is not a perfect cube.