Find the Value of the Product of x and Y

If 5x+9y=5 and 125x3+729y3=120 then the value of the product of x and y is:

  1. 45
  2. 135
  3. 1/9
  4. 1/135
Monis Rasool Professor Asked on 30th August 2015 in Maths.
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  • 1 Answer(s)

    Answer : (4) 1/135

    Explanation:-
    5x + 9y = 5                ……………….. (1)
    Cube on both side,
    (5x + 9y)3 = 53
    (5x)3 + (9y)3 + 3 x 5x X 9y (5x + 9y) = 125
    125x3 + 729y3 + 135 xy (5) = 125
    Put the value of 125x3 + 729y3 = 120        (Given in the question)
    Then, 120 + 135 x 5 xy = 125
    675 xy = 125 – 120
    xy = 5/675
    xy = 1/135
    Then, the value of the product of x and y is 1/135.

    Hence, the answer is (4) 1/135.

    Anurag Mishra Professor Answered on 31st August 2015.
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