Quadratic Equation


  1. With respect to the roots of x2 - x - 2 = 0, we can say that :









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    Given :- x2 - x - 2 = 0
    The given equation is of the form
    ax2 + bx + c = 0
    Here , a = 1 , b = -1 , c = - 2

    Correct Option: B

    Given :- x2 - x - 2 = 0
    The given equation is of the form
    ax2 + bx + c = 0
    Here , a = 1 , b = -1 , c = - 2
    Now, D2 = b2 - 4ac = ( -1 )2 - 4 x 1 x ( - 2 )
    D = √9 = 3
    So, roots are rational .
    Hence, both the roots must be integers.


  1. The roots of the equation7x2 - 6x - 13√7 = 0 are









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    Given that :- √7x2 - 6x - 13√7 = 0
    ⇒ √7x2 - 13x + 7x - 13√7 = 0
    ⇒ x( √7x - 13 ) + √7( √7x - 13 ) = 0
    ⇒ ( x + √7 ) ( √7x - 13 )
    ⇒ x + √7 = 0 or √7x - 13 = 0

    x = - √7or x =
    13
    =
    13 √7
    7
    7

    Correct Option: C

    Given that :- √7x2 - 6x - 13√7 = 0
    ⇒ √7x2 - 13x + 7x - 13√7 = 0
    ⇒ x( √7x - 13 ) + √7( √7x - 13 ) = 0
    ⇒ ( x + √7 ) ( √7x - 13 )
    ⇒ x + √7 = 0 or √7x - 13 = 0

    x = - √7or x =
    13
    =
    13 √7
    7
    7

    Thus, the two roots of given quadratic equation are

    - √7and
    13 √7
    .
    7



  1. In the following, find the value (s) of P so that the given equation has equal roots 3x 2 - 5x + P = 0









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    The given quadratic equation is
    3x2 - 5x + P = 0
    Comparing with ax 2 + bx + c = 0, we get
    a = 0, b = - 5, c = P
    If the given quadratic equation has equal roots then its discriminant = 0

    Correct Option: C

    The given quadratic equation is
    3x 2 - 5x + P = 0
    Comparing with ax 2 + bx + c = 0, we get
    a = 0, b = - 5, c = P
    If the given quadratic equation has equal roots then its discriminant = 0
    ⇒ b 2 - 4ac = 0
    ⇒ ( - 5 ) 2 - 4 x (3) x (P) = 0
    ⇒ 25 - 12P = 0

    ⇒ P =
    25
    12

    Hence , required answer is option C .


  1. 6 + √6 + √6 +........ is equal to









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    As per the given above question , we have
    Let, x = 6 + √6 + √6 + √6 +........
    On squaring both sides, we have
    x2 = 6 + √6 + √6 + √6 +........
    ⇒ x2 = 6 + x
    ⇒ x2 - x - 6 = 0

    Correct Option: D

    As per the given above question , we have
    Let, x = 6 + √6 + √6 + √6 +........
    On squaring both sides, we have
    x2 = 6 + √6 + √6 + √6 +........
    ⇒ x2 = 6 + x
    ⇒ x2 - x - 6 = 0
    ⇒ x2 - 3x + 2x - 6 = 0
    ⇒ x( x - 3 ) + 2( x - 3 ) = 0
    ⇒ ( x - 3 ) ( x + 2 ) = 0
    ⇒ x = 3 and x ≠ −2 because numbers are positive.
    Thus , correct answer will be 3 .



  1. If α, β are the roots of the quadratic equation x2 - 8x + k = 0, find the value of k such the α2 + β2 = 40









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    According to question ,
    ∵ α, β are the roots of the equation x2 - 8x + 1 = 0

    ∴ α + β =
    - b
    =
    - ( - 8 )
    = 8
    a
    1

    and αβ =
    c
    =
    k
    = k
    a
    1

    Now, α2 + β2 = ( α + β )2 - 2αβ

    Correct Option: A

    According to question ,
    ∵ α, β are the roots of the equation x2 - 8x + 1 = 0

    ∴ α + β =
    - b
    =
    - ( - 8 )
    = 8
    a
    1

    and αβ =
    c
    =
    k
    = k
    a
    1

    Now, α2 + β2 = ( α + β )2 - 2αβ
    ⇒ 40 = (8)2 -2k ⇒ 2k= 24 ⇒ k = 12.
    Thus , the value of k is 12 .