27
If x + y = 3, then what is the value of x3 + y3 + 9xy?
- A15
- B81
- C27
- D9
Answer not set
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CCommunity
Taking cube on both sides of x + y = 3 gives x3 + y3 + 3xy(x + y) = 27 ----(1)
And we know that x + y = 3
⇒ x3 + y3 + 3xy(x + y) = x3 + y3 + 3xy(3) = x3 + y3 + 9xy = 27 (From eq. 1)
∴ Value of x3 + y3 + 9xy = 27
And we know that x + y = 3
⇒ x3 + y3 + 3xy(x + y) = x3 + y3 + 3xy(3) = x3 + y3 + 9xy = 27 (From eq. 1)
∴ Value of x3 + y3 + 9xy = 27