If 2x + 3y = 9, and xy = 3, what is 8x3 + 27y3?
Show answer & explanation
Correct answer: C
Explanation
The correct answer is option 3 i.e. 243.
Given that
If 2x + 3y = 9, and xy = 3,
⇒ 2x + 3y = 9
⇒ Cube both sides
⇒ 8x3 + 27y3 + 18xy (2x + 3y) = 729
⇒ 8x3 + 27y3 + 18 × 3 × 9 = 729
⇒ 8x3 + 27y3 = 729 - 486
⇒ 8x3 + 27y3 = 243