Find the Value of Equation

If a3 + b3 = 9 and a + b = 3, then the value of  1/a+ 1/b  is

  1. 1/2
  2. 3/2
  3. 5/2
  4. -1
Manish Listener Asked on 16th June 2015 in Maths.
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  • 1 Answer(s)

    Answer: (2) 3/2
    Explanation:-
    (a + b)3 = a3 + b3 + 3ab(a + b)
    Put the value of a + b = 3   and a3 + b3 = 9
    Then, 33 = 9 + 3ab(3)
    27 – 9 = 9ab
    18 = 9ab
    ab = 2
    Now, 1/a + 1/b = (a + b)/ab
    Put the value of a + b = 3   and ab = 2
    Then, 3/2Hence, the answer is (2) 3/2.

    Anurag Mishra Professor Answered on 17th June 2015.
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