Question : If a3 + b3 = 217 and a + b = 7, then the value of ab is:
Option 1: – 6
Option 2: – 1
Option 3: 7
Option 4: 6
Correct Answer: 6
Solution : According to the question a 3 + b 3 = 217 and, a + b = 7 Now, (a + b) 3 = a 3 + b 3 + 3ab (a + b) ⇒ 7 3 = 217 + 3ab (7) ⇒ 343 – 217 = 21ab ⇒ $\frac{126}{21}$ = ab ⇒ ab = 6 Hence, the correct answer is 6.
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