Question 64

If $$x - \frac{1}{x} = 11$$, then $$x^3 - \frac{1}{x^3}$$ is:

Solution

$$x - \frac{1}{x} = 11$$

$$x^3 - \frac{1}{x^3}$$ = $$(x - \frac{1}{x})^3 - 3(x - \frac{1}{x})$$

($$\because (a - b)^3 = a^3 - b^3 -3ab(a - b)$$)

= $$(11)^3 - 3(11)$$

= 1331 - 33 = 1298


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