A) 3
B) 7
C) 11
D) 18
Correct Answer: D
Solution :
[d] \[If\,\,{{x}^{2}}-\,3x+1=0\,\,then\,\,{{x}^{3}}+\frac{1}{{{x}^{3}}}=?\] Dividing equation by x \[x-\,3+\frac{1}{x}=0\] \[x+\,\frac{1}{x}=3\] \[\therefore \,\,{{x}^{3}}+\frac{1}{{{x}^{3}}}={{\left( x+\frac{1}{x} \right)}^{3}}-3\,\,\left( x+\frac{1}{x} \right)\] \[={{(3)}^{3}}-\,3\times 3\] \[=27-\,9\] \[=18\]You need to login to perform this action.
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