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
Answer (1)
20th Jan, 2024
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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