Question

Find the cube of 5 -1/7

Answer 1

5³-1/7³-3×5×-1/7(5-1/7)
125-1/343-15/7×34

Answer 2

$\textbf{ANSWER:}$

According to the identity:

${(x - y)}^{3} = {x}^{3} - {y}^{3} - 3 {x}^{2} y + 3x {y}^{2}$

Taking:

5 = x
And
1/7 = y

${(5 - \frac{1}{7}) }^{3} = {5}^{3} - { \frac{1}{7} }^{3} - 3 \times {5}^{2} \times \frac{1}{7} + 3 \times 5 \times { (\frac{1}{7} })^{2} \\ \\ = 》 125 - \frac{1}{343} - \frac{75}{7} + \frac{15}{49} \\ \\ = 》 \frac{42875 - 1 - 3675 + 105}{343} \\ \\ = 》 \frac{39304}{343}$

That's the answer...