Quadratic Equation


  1. The sum of a number and its reciprocal is 10/3, then the numbers are









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    Let the number be x and 1/x,
    Then, x + 1/x = 10/3
    ⇒ x2 + 1/x = 10/3

    Correct Option: A

    Let the number be x and 1/x,
    Then, x + 1/x = 10/3
    ⇒ (x2 + 1)/x = 10/3
    ⇒ 3x2 - 10x + 3 = 0
    ⇒ 3x2 - 9x - x + 3 = 0
    ⇒ 3x(x - 3) -1 (x - 3) = 0
    ⇒ (3x - 1) (x - 3) = 0
    ∴ x = 1/3, x = 3


  1. The values of p for which the difference between the roots of the equation x2 + px + 8 = 0 is 2 , are











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    α + β = - p, α β = 8
    Given, α - β = 2
    On squaring both sides, we get
    (α - β)2 = 4

    Correct Option: C

    α + β = - p, α β = 8
    Given, α - β = 2
    On squaring both sides, we get
    (α - β)2 = 4
    ⇒ (α + β)2 - 4αβ = 4
    ⇒ p2 - 32 = 4
    ⇒ p2 = 36 ⇒ p = ± 6



Direction: In each of the following question, there are two equations. you have to solve both equations and give answer.

  1. x2 + x - 20 = 0
    y2 - y - 30 = 0











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    x2 + x - 20 = 0
          [by factorisation method]
    (x + 5) (x - 4) = 0

    and y2 - y - 30 = 0
    ⇒ (y - 6) (y + 5) = 0

    Correct Option: D

    x2 + x - 20 = 0
          [by factorisation method]
    ⇒ x2 + 5x - 4x - 20 = 0
    ⇒ x(x + 5) - 4(x + 5) = 0
    (x + 5) (x - 4) = 0
    ∴ x = -5 or 4
    and y2 - y - 30 = 0
    ⇒ y2 - 6y + 5y - 30 = 0
    ⇒ y(y - 6) + 5(y - 6) = 0
    ⇒ (y - 6) (y + 5) = 0
    ∴ y = 6 or - 5
    Hence, y ≥ x or x ≤ y


  1. If x2 - 3x + 1 = 0, find the value of x + 1/x,









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    Given equation is
    x2 - 3x + 1 = 0 ⇒ x2 + 1 = 3x
    ⇒ x2 + 1/x = 3
    ⇒ x2/x + 1/x = 3
    ∴ x + 1/x = 3

    Correct Option: B

    Given equation is
    x2 - 3x + 1 = 0 ⇒ x2 + 1 = 3x
    ⇒ x2 + 1/x = 3
    ⇒ x2/x + 1/x = 3
    ∴ x + 1/x = 3



  1. x - √121 = 0
    y2 - 121 = 0











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    x - √121 = 0
    ⇒ x = √121 ⇒ x = ± 11
    and y2 - 121 = 0 ⇒ y2 = 121
    ⇒ y = √121 = ± 11
    ∴ x = y

    Correct Option: E

    x - √121 = 0
    ⇒ x = √121 ⇒ x = ± 11
    and y2 - 121 = 0 ⇒ y2 = 121
    ⇒ y = √121 = ± 11
    ∴ x = y