Question
If, a 3 + b 3 = 485 and a + b =
5, then find the value of (1/a) + (1/b) .Solution
We know that, (x + y) 3 = x 3 + y 3 + 3xy X (x + y)
So, (a + b) 3 = a 3 + b 3 + 3ab X (a + b)
Or, 5 3 = 485 + 3 X ab X 5
Or, 15ab = 125 - 485
Or, ab = - (360/15)
So, ab = - 24
(1/a) + (1/b) = (a + b) ÷ ab
= 5 ÷ ( - 24) = - (5/24)
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