Difference of two perfect cube is $189$. If the cube root of the smaller of the two numbers is $3$, then find the cube root of the larger number.


Given: Difference of two perfect cube is $189$. If the cube root of the smaller of the two numbers is $3$. 

To do: To find the cube root of the larger number.

Solution:

Let $x$ and $y$ be the cube roots of the larger and smaller number respectively.

As given difference of two numbers which are perfect cubes is $189$.

$\Rightarrow x^3-y^3=189$

If  $y$ is the cube root of the smaller number.

$\Rightarrow y=3$

$\Rightarrow y^3=27$

$\Rightarrow x^3-y^3=189$

$\Rightarrow x^3 -27=189$             [On putting the value of $y^3=27$]

$\Rightarrow x^3=189+27$

$\Rightarrow x^3=216$

$\Rightarrow  x=\sqrt[3]{216}$

$\Rightarrow x=\sqrt[3]{6\times6\times6}$

$\Rightarrow x=6$

Therefore, cube root of the larger number is $6$.

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Updated on: 10-Oct-2022

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