A) 243
B) 343
C) 441
D) 729
Correct Answer: B
Solution :
By question, \[x+y=7\] Then, \[{{x}^{3}}+{{y}^{3}}+21xy\] \[={{(x+y)}^{3}}-3xy\,\,(x+y)+21xy\] \[={{(7)}^{3}}-3xy\,\,(7)+21xy\] \[=343-21xy+21xy=343\]You need to login to perform this action.
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