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Home Aptitude Quadratic Equation Comments

  • Question
  • Two students A and B solve an equation of the from x 2 + px + q = 0. A starts with a wrong value of p and obtains the roots as 2 and 6. B starts with a wrong value of q and gets the roots as 2 and -9. What are the correct roots of the equation?


  • Options
  • A. 3 and - 4
  • B. - 3 and - 4
  • C. - 3 and 4
  • D. 3 and 4

  • Correct Answer
  • - 3 and - 4 

    Explanation

    Let ? and ? be the roots of the quadratic equation x2 + px + q = 0
    Given that, A starts with a wrong value of p and obtains the roots as 2 and 6. But this time q is correct. i.e products of roots
    = q = ? . ? = 6 x 2 = 12 ...(i)
    and B starts with a wrong value of q and gets the roots as 2 and - 9. But this time p is correct i.e., sum of roots
    = p = ? + ? = - 9 + 2 = - 7 ..(ii)
    (? - ?)2 = (? + ?)2 - 4? ?
    = (-7)2 - 4.12 = 49 - 48 = 1
    [from Eqs. (i) and (ii)]
    ? ? - ? = 1 ..(iii)
    Now, from Eqs. (ii) and (iii) , we get
    ? = - 3 and ? = - 4
    which are correct roots .


  • Quadratic Equation problems


    Search Results


    • 1. 
      If one of the roots of the equation x 2 - bx + c = 0 is the square of the other, then which of the following option is correct?

    • Options
    • A. b3 = 3bc + c2 + c
    • B. c3 = 3bc + b2 + b
    • C. 3bc = c3 + b2 + b
    • D. 3bc = c3 + b3 + b2
    • Discuss
    • 2. 
      In solving a problem, one student makes a mistake in the coefficient of the first degree term and obtain -9 and -1 for the roots. Another student makes a mistake in the constant term of the equation and obtains 8 and 2 for the roots. The correct equation was

    • Options
    • A. x2 + 10x + 9 = 0
    • B. x2 - 10x + 16 = 0
    • C. x2 - 10x + 9 = 0
    • D. None of the above
    • Discuss
    • 3. 
      If ? and ? are the roots of the equation 8x 2 - 3x + 27 = 0, find the value of (? 2/?) 1/3 + (? 2/?) 1/3

    • Options
    • A. 1/3
    • B. 1/4
    • C. 7/2
    • D. 4
    • Discuss
    • 4. 
      The sum of the roots of the equation x 2 + px + q = 0 is equal to the sum of their squares, then

    • Options
    • A. p2 - q2 = 0
    • B. p2 + q2 = 2q
    • C. p2 + p = 2q
    • D. q2 + q2 = 2p
    • Discuss
    • 5. 
      If a = p / (p + q) and b = q / (p - q), then and ab/a + b is equal to

    • Options
    • A. pq / (p2 + q2)
    • B. (p2 + q2) / pq
    • C. p / (p + q)
    • D. [p / (p + q)]2
    • Discuss
    • 6. 
      If x = ? ?(5 + 1)/?(5 - 1), then x 2 - x - 1 is equal to

    • Options
    • A. 0
    • B. 1
    • C. 2
    • D. 5
    • Discuss
    • 7. 
      If ?, ? are the roots of the equation x2 - 5x + 6 = 0, construct a quadratic equation whose roots are
      1
      ,
      1
      .
      ?
      ?

    • Options
    • A. 6x2 + 5x - 1 = 0
    • B. 6x2 - 5x - 1 = 0
    • C. 6x2 - 5x + 1 = 0
    • D. 6x2 + 5x + 1 = 0
    • Discuss
    • 8. 
      Consider the equation px2 + qx + r = 0, where p, q, r are real. The roots are equal in magnitude but opposite in sign when :

    • Options
    • A. q = 0, r = 0, p ? 0
    • B. p = 0, qr ? 0
    • C. r = 0, pr ? 0
    • D. q = 0, pr ? 0
    • Discuss
    • 9. 
      The roots of the equation 4x - 3 × 2x × 22 + 32 = 0 would include :

    • Options
    • A. 1, 2 and 3
    • B. 1 and 2
    • C. 1 and 3
    • D. 2 and 3
    • Discuss
    • 10. 
      Find the value of k so that the sum of the roots of the equation 3x2 + (2x + 1)x - k - 5 = 0 is equal to the product of the roots :

    • Options
    • A. 4
    • B. 6
    • C. 2
    • D. 8
    • Discuss


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