If (0.4x + 1/x ) = 5, wat is the value of (0.064x³ + 1/(x³) )?

If (0.4x + 1/x ) = 5, wat is the value of (0.064x³ +…

If (0.4x + $\frac{1}{x}$ ) = 5, wat is the value of (0.064x³ + $\frac{1}{x^3}$ )?

Show answer & explanation

Correct answer: B

Explanation

The correct answer is option 2 i.e. 119

Formula used:

(a + b)³ = a³ + b³ + 3ab(a + b) ---- (1)

Calculations:

⇒ (0.4x + $\frac{1}{x}$ )³ = 0.064x³ + 1/x³ + 3 × 0.4 × (0.4x + $\frac{1}{x}$ )

⇒ 5³ = 0.064x³ + 1/x³ + 3 × 0.4 × 5

⇒ 125 = 0.064x³ + 1/x³ + 6

⇒ 0.064x³ + 1/x³ = 119