If (x + 6y) = 8, and xy = 2, where x > 0, what is the value of (x3 + 216y3)?
Show answer & explanation
Correct answer: C
Explanation
The correct answer is option 3 i.e. 224
We have given,
(x + 6y) = 8, and xy = 2
x + 6y = 8
Cubing on both sides
⇒ x3 + 216 y3 + 18xy(x + 6y) = 512
⇒ x3 + 216 y3 + 18 × 2 × (8) = 512
⇒ x3 + 216 y3 = 512 - 288 = 224