A) 207
B) 198
C) 199
D) 208
Correct Answer: B
Solution :
[b] \[x+y=6\text{ }and\text{ }xy=1\] \[\therefore \,\,{{x}^{3}}+{{y}^{-3}}=\frac{1}{{{x}^{3}}}+\frac{1}{{{y}^{3}}}=\frac{{{x}^{3}}+{{y}^{3}}}{{{(xy)}^{3}}}\] \[{{x}^{3}}+{{y}^{3}}={{(x+y)}^{3}}-3xy(x+y)\] \[={{6}^{3}}-3.1.6=198\] \[\therefore \,{{x}^{-3}}+{{y}^{-3}}=\frac{198}{1}=198.\]You need to login to perform this action.
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