If x4 - 83x² + 1 = 0, then the value of (x³ - x-3) can be ?
Show answer & explanation
Correct answer: B
Explanation
The correct answer is option 2 ie 756.
x4 - 83x² + 1 = 0
x² + (1/x²) = 83
x - (1/x) = 9 = k
⇒ x³ - (1/x³) = k³ + 3k
= 9³ + (3 × 9)
= 9 (81 + 3)
= 9 × 84
= 756