Question : a3 – b3 = 91 and a – b = 1, what is the value of (ab)?
Option 1: 27
Option 2: 6
Option 3: 9
Option 4: 30
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Answer (1)
23rd Jan, 2024
Correct Answer: 30
Solution :
Given: a
3
– b
3
= 91 and a – b = 1
Then (a – b)
3
= (1)
3
⇒ a
3
– b
3
– 3ab(a – b) = 1
⇒ 91 – 3ab(1) = 1
⇒ 3ab = 90
$\therefore$ ab = 30
Hence, the correct answer is 30.
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