Question : If (a – b) = 1 and ab = 6, then what is the value of (a3 – b3)?
Option 1: 21
Option 2: 23
Option 3: 19
Option 4: 25
Correct Answer: 19
Solution :
Given:
(a – b) = 1
ab = 6
We know, a
3
– b
3
= (a – b)
3
+ 3ab(a – b)
⇒ a
3
– b
3
= (1)
3
+ (3 × 6 × 1) = 1 + 18 = 19
Hence, the correct answer is 19.
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