Question

If [5x + 1/(3x)] = (-10/3); find the value of [(3x)³ + 1/(5x)³]?
1. -4.4
2. -4.8
3. -4
4. -4.2

Answer 1

Correct Answer - Option 1 : -4.4

Given:

[5x + 1/(3x)] = (-10/3)

Calculation:

∵ [5x + 1/(3x)] = (-10/3)

Multiplying both side with 3/5;

⇒ 3/5 × [5x + 1/(3x)] = 3/5 × (-10/3)

⇒ [(3/5) × (5x)] + [(3/5) × (1/3x)] = (-2)

⇒3x + (1/5x) = (-2)

Cube both side;

⇒ (3x)³ + (1/5x)³ + 3 × (3x) × (1/5x) × [3x + (1/5x)] = (-8)

⇒ (3x)³ + (1/5x)³ + [9/5 × (-2)] = (-8)

⇒ (3x)³ + (1/5x)³ – (18/5) = (-8)

⇒ (3x)³ + (1/5x)³ = (-8) + (18/5)

⇒ (3x)³ + (1/5x)³ = [(-40) + 18]/5

⇒ (3x)³ + (1/5x)³ = (-22)/5

⇒ (3x)³ + (1/5x)³ = (-4.4)