If (a - b) = 9, and (a3 - b3) = 4401, find the value of ab.
Show answer & explanation
Correct answer: D
Explanation
The correct answer is option 4 i.e. 136.
Given:
(a - b) = 9
(a3 - b3) = 4401
Formula used:
(a - b)3 = a3 - b3 - 3ab(a - b)
Calculations:
According to the question;
⇒ (a - b)3 = a3 - b3 - 3ab(a - b)
⇒ 93 = 4401 - 3ab(9)
⇒ 729 = 4401 - 27ab
⇒ 27ab = 4401 - 729
⇒ ab = 136