If x + y = 3 then what is the value...

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If x + y = 3, then what is the value of x³ + y³ + 9xy?

A. 15

B. 81

C. 27

D. 9

Answer: Option C

Solution(By Examveda Team)

x + y = 3
Put x = 1, y = 2
x³ + y³ + 9xy
= (1)³ + (2)³ + 9 × 2 × 1
= 1 + 8 + 18
= 27

Alternate:
x + y = 3 . . . . . . (1)
On taking cube on both sides
(x + y)³ = (3)³
x³ + y³ + 3xy(x + y) = 27
x³ + y³ + 3xy(3) = 27
x³ + y³ + 9xy = 27

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