If x + y = 7, then the value of x3 + y3 + 21xy is?
A. 243
B. 143
C. 343
D. 443
Answer: Option C
Solution(By Examveda Team)
$$\eqalign{ & x + y = 7 \cr & \left( {{\text{cubing both sides}}} \right){\text{ }} \cr & \Rightarrow {\left( {x + y} \right)^3} = {\left( 7 \right)^3} \cr & \Rightarrow {x^3} + {y^3} + 3\left( {x + y} \right)xy = 343 \cr & \Rightarrow {x^3} + {y^3} + 21xy = 343 \cr} $$This Question Belongs to Arithmetic Ability >> Algebra
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