Quadratic Equation


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

  1. 225x2 - 4 = 0;       √225y + 2 = 0











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    Solve both equation and find the value of x and y.

    Correct Option: E

    225x2 - 4 = 0;
    ⇒ 225x2 = 4 ⇒ x2 = 4/225
    ∴ x = √4/225 = ± 2/15, i.e., 2/15 and -2/15
    and √225y + 2 = 0 or √225y = -2
    On squaring both sides, we get
    (√225y)2 = (-2)2
    ⇒ 225y = 4
    ∴ y = 4/225
    So, relation cannot be established because 4/225 lies between 2/15 and -2/15.


  1. If one of the roots of quadratic equation 7y2 - 50y + k = 0 is 7, then what is the value of k ?









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    Given quadratic equation is
    7y2 - 50y + k = 0
    If one root is 7, then it will satisfy the equation i.e putting y = 7 in equation
    7 x (7)2 - 50 x 7 + k = 0

    Correct Option: A

    Given quadratic equation is
    7y2 - 50y + k = 0
    If one root is 7, then it will satisfy the equation i.e putting y = 7 in equation
    7 x (7)2 - 50 x 7 + k = 0
    ⇒ 7 x 49 - 350 + k = 0
    ⇒ 343 - 350 + k = 0
    ∴ k = 7



  1. For what value of k, the equation x2 + 2(k - 4) x + 2k = 0 has equal roots ?











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    Given equation is
    x2 + 2(k - 4)x + 2k = 0
    On comparing with ax2 + bx + c = 0
    Here, a = 1, b = 2(k -4), c = 2k
    Since, the root are equal, we have D = 0.
    b2 - 4ac = 0

    Correct Option: B

    Given equation is
    x2 + 2(k - 4)x + 2k = 0
    On comparing with ax2 + bx + c = 0
    Here, a = 1, b = 2(k -4), c = 2k
    Since, the root are equal, we have D = 0.
    b2 - 4ac = 0
    ∴ 4(k - 4)2 - 8k = 0
    4(k2 + 16 - 8k) - 8k = 0
    ⇒ 4k2 + 64 - 32k - 8k = 0
    ⇒ 4k2 - 40k + 64 = 0
    ⇒ k2 - 10k + 16 = 0
    ⇒ k2 - 8k - 2k + 16 = 0
    ⇒ k(k - 8) -2 (k - 8) = 0
    ⇒ (k - 8) (k - 2) = 0
    Hence, the value of k 8 or 2.


  1. The quadrictic equation whose roots are 3 and -1, is









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    Given that, the roots of the quadrictic equation are 3 and -1.
    Let α = 3 and β = -1
    Sum of roots = α + β = 3 - 1 = 2
    Products of roots = α . β = (3) (-1) = -3
    ∴ Required quadric equation is
    x2 - (α + β)x + α β = 0

    Correct Option: B

    Given that, the roots of the quadrictic equation are 3 and -1.
    Let α = 3 and β = -1
    Sum of roots = α + β = 3 - 1 = 2
    Products of roots = α . β = (3) (-1) = -3
    ∴ Required quadric equation is
    x2 - (α + β)x + α β = 0
    ⇒ x2 - (2)x + (-3) = 0
    ⇒ x2 - 2x - 3 = 0



  1. If α and β are the roots of the equation 4x2 - 19x + 12 = 0, find the equation having the roots 1/α and 1/β











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    Given equation is 4x2 - 19x + 12 = 0
    Let given equation having the roots 1/α and 1/β,
    Then required equuation is
    12x2 - 19x + 4 = 0

    Correct Option: B

    Given equation is 4x2 - 19x + 12 = 0
    Let given equation having the roots 1/α and 1/β,
    Then required equuation is
    12x2 - 19x + 4 = 0