If a3 + b3 = 405 a + b = 9 , then the value of ab is
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Correct answer: D
Explanation
The correct answer is option 4 i.e. 12
Given :
a3 + b3 = 405 and a + b = 9
Formula used :
(a + b)3 = a3 + b3 + 3ab(a + b) ---- (1)
Calculations :
Using equation (1), we get
⇒ (9)3 = 405 + 3ab(9)
⇒ 729 = 405 + 27ab
⇒ 324 = 27ab
⇒ ab = 12