MCQ
If $x = {2^{1/3}} - {2^{ - 1/3}},$ then $2{x^3} + 6x = $
- A$1$
- B$2$
- ✓$3$
- DNone of these
✓
Answer
Correct option: C.
$3$
c
(c) $x = {2^{1/3}} - {2^{ - 1/3}}$
(c) $x = {2^{1/3}} - {2^{ - 1/3}}$
$ \Rightarrow $${x^3} = 2 - {2^{ - 1}} - {3.2^{1/3}}{.2^{ - 1/3}}({2^{1/3}} - {2^{ - 1/3}})$
$ \Rightarrow $${x^3} = 2 - {1 \over 2} - 3x$ ==> ${x^3} + 3x = {3 \over 2}$
$\therefore 2{x^3} + 6x = 3$.
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