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  • Question
  • If a = ( ?2 -1)1/3, then the value of (a - a-1)3 + 3 ( a - a -1 ) is?


  • Options
  • A. -2
  • B. 2
  • C. 2?2
  • D. ?2

  • Correct Answer
  • -2 

    Explanation

    Given that,
    a = (?2 - 1)1/3
    By cubing the both side of the given equation.
    a3 = ?2 - 1
    Then 1/a3 = 1/?2 - 1
    Now multiply and divide the above equation by ?2 + 1
    ? 1/a3 = ( ?2 + 1 ) / ( ?2 + 1 ) x 1/(?2 - 1 )
    ? 1/a3 = ( ?2 + 1 ) x 1 / ( ?2 + 1 ) x (?2 - 1 ) [ Use the formula (A + B)(A - B) = A2 - B2 ]
    ? 1/a3 = ( ?2 + 1 ) / ( 2 - 1 )
    ? 1/a3 = ?2 + 1
    According to the question
    ( a - a-1 )3 + 3 ( a - a-1 )
    = (a - 1/a)3 + 3(a - 1/a) Use the formula [ ( A - B)3 = A3 - B3 + 3AB(A - B) ]
    = a3 - 1/a3 - 3 a x 1/a (a -1/a) + 3(a - 1/a)
    = a3 - 1/a3 - 3 (a -1/a) + 3(a - 1/a)
    = a3 - 1/a3
    Pu the value of a3 and 1/a3
    = ?2 -1 - ( ?2 + 1 )
    = ?2 -1 - ?2 - 1
    = -2


  • Simplification problems


    Search Results


    • 1. 
      If ?28 - 6?3 = ?3a + b, (where a, b are rationals), value of (a + b) is?

    • Options
    • A. -2
    • B. 2
    • C. 1
    • D. -1
    • Discuss
    • 2. 
      If x + a/x = 1, then the value of ( x2 + x + a ) / (x3 - x2) is?

    • Options
    • A. -2
    • B. -a/2
    • C. 2/a
    • D. -2/a
    • Discuss
    • 3. 
      1/(1 x 4) + 1/(4 x 7) + 1/(7 x 10) + 1/(10 x 13) + 1/(13 x 16) =?

    • Options
    • A. 5/16
    • B. 3/16
    • C. 7/16
    • D. 11/16
    • Discuss
    • 4. 
      If x = ( ?2 + 1 ) / ( ?2 - 1 ) and x - y = 4?2, then the value of (x2 + y2) is?

    • Options
    • A. 34
    • B. 38
    • C. 30
    • D. 32
    • Discuss
    • 5. 
      ( 8.73 x 8.73 x 8.73 + 4.27 x 4.27 x 4.27 ) / ( 8.73 x 8.73 - 8.73 x 4.27 + 4.27 x 4.27 ) is equal to?

    • Options
    • A. 11
    • B. 13
    • C. 11/7
    • D. None of these
    • Discuss
    • 6. 
      If x = ( ? 3 + 1 ) / ( ? 3 - 1 ) and y = ( ? 3 - 1) / ( ? 3 + 1 ) , then the value of x2/y + y2/x is?

    • Options
    • A. 52
    • B. 76
    • C. 4
    • D. 64
    • Discuss
    • 7. 
      If x + a/x = b , then the value of ( x2 + bx + a) / ( bx2 - x3 ) is?

    • Options
    • A. a + b
    • B. 2b/a
    • C. b/a
    • D. ab
    • Discuss
    • 8. 
      51.3 + 7.078 +1.38 + 0.9 =?

    • Options
    • A. 61.668
    • B. 59.238
    • C. 60.658
    • D. None of these
    • Discuss
    • 9. 
      The product of 3.5413 x 2.1 is

    • Options
    • A. 7.44673
    • B. 7.43673
    • C. 7.53673
    • D. None of these
    • Discuss
    • 10. 
      [( 3.242 x 14 ) / 100] =?

    • Options
    • A. 0.045388
    • B. 4.5388
    • C. 453.88
    • D. None of these
    • Discuss


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