Given:
The expression is:
[tex]\left(\dfrac{1}{7}-4\sqrt{3}\right)^3+\left(\dfrac{1}{7}+4\sqrt{3}\right)^3 [/tex]
To find:
The simplified form of the given expression.
Solution:
Formulae used:
[tex](a-b)^3=a^3-3a^2b+3ab^2-b^3[/tex]
[tex](a-b)^3=a^3+3a^2b+3ab^2+b^3[/tex]
Adding this formulae, we get
[tex](a-b)^3+(a+b)^3=2a^3+6ab^2[/tex] ...(i)
We have,
[tex]\left(\dfrac{1}{7}-4\sqrt{3}\right)^3+\left(\dfrac{1}{7}+4\sqrt{3}\right)^3 [/tex]
Using formula (i), the given expression can be written as:
[tex]=2\left(\dfrac{1}{7}\right)^3+6\left(\dfrac{1}{7}\right)\left(4\sqrt{3}\right)^2[/tex]
[tex]=2\times \dfrac{1}{343}+6\left(\dfrac{1}{7}\right)48[/tex]
[tex]=\dfrac{2}{343}+\dfrac{288}{7}[/tex]
[tex]=\dfrac{2+14112}{343}[/tex]
[tex]=\dfrac{14114}{343}[/tex]
Therefore, the simplified form of the given expression is [tex]\dfrac{14114}{343}[/tex].
