
Which of the following are the perfect cubes?
A. $729$
B. $10000$
C. $1729$
D. none of these
Answer
464.1k+ views
Hint: To obtain which of the given numbers is a perfect cube we will use prime factorization method. Firstly we will find the prime factor of the number and then we will check whether we are getting a product of all the numbers multiplied by itself three times. If yes it is a perfect cube otherwise not.
Complete step-by-step answer:
We will check for each option given as follows:
Option (A)
We have to whether the below number is a perfect cube:
$729$
So we will find the prime factor of the number as follows:
$\begin{align}
& 3\left| \!{\underline {\,
729 \,}} \right. \\
& 3\left| \!{\underline {\,
243 \,}} \right. \\
& 3\left| \!{\underline {\,
81 \,}} \right. \\
& 3\left| \!{\underline {\,
27 \,}} \right. \\
& 3\left| \!{\underline {\,
9 \,}} \right. \\
& 3\left| \!{\underline {\,
3 \,}} \right. \\
& 1 \\
\end{align}$
So we get the prime factors as:
$729=3\times 3\times 3\times 3\times 3\times 3$
We can rewrite it as:
$729={{3}^{3}}\times {{3}^{3}}$
We are getting two terms which are multiplied by it-self three times so:
$729={{9}^{3}}$
So we get that 729 is a perfect cube.
Option (B)
We have to whether the below number is a perfect cube:
$10000$
So we will find the prime factor of the number as follows:
$\begin{align}
& 2\left| \!{\underline {\,
10000 \,}} \right. \\
& 2\left| \!{\underline {\,
5000 \,}} \right. \\
& 2\left| \!{\underline {\,
2500 \,}} \right. \\
& 2\left| \!{\underline {\,
1250 \,}} \right. \\
& 5\left| \!{\underline {\,
625 \,}} \right. \\
& 5\left| \!{\underline {\,
125 \,}} \right. \\
& 5\left| \!{\underline {\,
25 \,}} \right. \\
& 5\left| \!{\underline {\,
5 \,}} \right. \\
& 1 \\
\end{align}$
So we get the prime factors as:
$10000=2\times 2\times 2\times 2\times 5\times 5\times 5\times 5$
We can rewrite it as:
$10000={{2}^{4}}\times {{5}^{4}}$
We are getting two terms multiplied four times by it-self.
So we get that 10000 is not a perfect cube.
Option (C)
We have to whether the below number is a perfect cube:
$1729$
So we will find the prime factor of the number as follows:
$\begin{align}
& 7\left| \!{\underline {\,
1729 \,}} \right. \\
& 13\left| \!{\underline {\,
247 \,}} \right. \\
& 19\left| \!{\underline {\,
19 \,}} \right. \\
& 1 \\
\end{align}$
So we get the prime factors as:
$1729=7\times 13\times 19$
We are not getting cube of any term
So we get that 1729 is not a perfect cube.
So, the correct answer is “Option A”.
Note: Factors of any number is a number which divide it completely. When we are talking about prime factorization we involve only prime numbers as a factor. This method is widely used to find the square root or cube root of any number. When we multiply a number by it-self three times the number obtained is known as cube of that number.
Complete step-by-step answer:
We will check for each option given as follows:
Option (A)
We have to whether the below number is a perfect cube:
$729$
So we will find the prime factor of the number as follows:
$\begin{align}
& 3\left| \!{\underline {\,
729 \,}} \right. \\
& 3\left| \!{\underline {\,
243 \,}} \right. \\
& 3\left| \!{\underline {\,
81 \,}} \right. \\
& 3\left| \!{\underline {\,
27 \,}} \right. \\
& 3\left| \!{\underline {\,
9 \,}} \right. \\
& 3\left| \!{\underline {\,
3 \,}} \right. \\
& 1 \\
\end{align}$
So we get the prime factors as:
$729=3\times 3\times 3\times 3\times 3\times 3$
We can rewrite it as:
$729={{3}^{3}}\times {{3}^{3}}$
We are getting two terms which are multiplied by it-self three times so:
$729={{9}^{3}}$
So we get that 729 is a perfect cube.
Option (B)
We have to whether the below number is a perfect cube:
$10000$
So we will find the prime factor of the number as follows:
$\begin{align}
& 2\left| \!{\underline {\,
10000 \,}} \right. \\
& 2\left| \!{\underline {\,
5000 \,}} \right. \\
& 2\left| \!{\underline {\,
2500 \,}} \right. \\
& 2\left| \!{\underline {\,
1250 \,}} \right. \\
& 5\left| \!{\underline {\,
625 \,}} \right. \\
& 5\left| \!{\underline {\,
125 \,}} \right. \\
& 5\left| \!{\underline {\,
25 \,}} \right. \\
& 5\left| \!{\underline {\,
5 \,}} \right. \\
& 1 \\
\end{align}$
So we get the prime factors as:
$10000=2\times 2\times 2\times 2\times 5\times 5\times 5\times 5$
We can rewrite it as:
$10000={{2}^{4}}\times {{5}^{4}}$
We are getting two terms multiplied four times by it-self.
So we get that 10000 is not a perfect cube.
Option (C)
We have to whether the below number is a perfect cube:
$1729$
So we will find the prime factor of the number as follows:
$\begin{align}
& 7\left| \!{\underline {\,
1729 \,}} \right. \\
& 13\left| \!{\underline {\,
247 \,}} \right. \\
& 19\left| \!{\underline {\,
19 \,}} \right. \\
& 1 \\
\end{align}$
So we get the prime factors as:
$1729=7\times 13\times 19$
We are not getting cube of any term
So we get that 1729 is not a perfect cube.
So, the correct answer is “Option A”.
Note: Factors of any number is a number which divide it completely. When we are talking about prime factorization we involve only prime numbers as a factor. This method is widely used to find the square root or cube root of any number. When we multiply a number by it-self three times the number obtained is known as cube of that number.
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