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If x - 1/x = 20 then find the value of  (x3 - 1/x3)


1. 7900
2. 8060
3. 8000
4. 7960

1 Answer

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Best answer
Correct Answer - Option 2 : 8060

Given

(x - 1/x) = 20

Formula used

(a - b)3 = a3 - b3 - 3ab × (a - b)

Calculation

(x - 1/x)3 = x3 - 1/x3 - 3(x)(1/x)(x - 1/x)

⇒ 203 = x3 - 1/x3 - 3(20)

⇒ x3 - 1/x3 = 8060

∴ x3 - 1/x3 = 8060

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