If (x + y) : (x - y) = 5 : 2, find (x3 + y3) : (x3 – y3)
Show answer & explanation
Correct answer: A
Explanation
The correct answer is option 1 i.e. 185 : 158.
(x + y)/(x - y) = 5/2
⇒ 2x + 2y = 5x - 5y
⇒ 3x = 7y
⇒ x/y = 7/3
⇒ (x/y)3 = (7/3)3
⇒ x3/y3 = 343/27
⇒ (x3 + y3) : (x3 – y3) = (343/27 + 1) : (343/27 – 1)
= (370/27) : (316/27)
= 370 : 316
= 185 : 158