SSC CHSL 2021 · PYQ · Algebra · medium
If x² + 1/x² = 83, x > 0, then the value of x³ – 1/x³ is:
Answer
The correct answer is D: 756. x² + 1/x² = 83, so (x – 1/x)² = 83 – 2 = 81, x – 1/x = 9. Then x³ – 1/x³ = (x – 1/x)³ + 3(x – 1/x) = 729 + 27 = 756.
- A.785
- B.576
- C.675
- D.756✓ Correct
x² + 1/x² = 83, so (x – 1/x)² = 83 – 2 = 81, x – 1/x = 9. Then x³ – 1/x³ = (x – 1/x)³ + 3(x – 1/x) = 729 + 27 = 756.
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