Quadratic Equation


  1. If a and b are the roots of the equation x2 - 6x + 6 = 0, find the value of 2(a2 + b2).











  1. View Hint View Answer Discuss in Forum

    a and b are the roots of the equation
    x2 - 6x + 6 = 0
    ∴ a + b = -B/A = 6 and ab = C/A = 6

    Correct Option: C

    a and b are the roots of the equation
    x2 - 6x + 6 = 0
    ∴ a + b = -B/A = 6 and ab = C/A = 6
    We know that,
    a2 + b2 = (a + b)2 - 2ab
    = (6)2 - 2 x 6 = 36 - 12 = 24
    ∴ 2(a2 + b2) = 2 x 24 = 48


  1. If α, β are the roots of the equation x2 - 5x + 6 = 0, construct a quadratic equation whose roots are
    1
    ,
    1
    .
    α
    β









  1. View Hint View Answer Discuss in Forum

    As per the given above question , we can say that
    Comparing x2 - 5x + 6 = 0 with ax2 - bx + c = 0 , we get
    a = 1, b = - 5, c = 6

    ∴ α + β =
    - b
    =
    5
    = 5
    a
    1

    αβ =
    c
    = 6
    a

    Now, we are to form an equation whose roots are
    1
    ,
    1
    .
    α
    β

    Correct Option: C

    As per the given above question , we can say that
    Comparing x2 - 5x + 6 = 0 with ax2 - bx + c = 0 , we get
    a = 1, b = - 5, c = 6

    ∴ α + β =
    - b
    =
    5
    = 5
    a
    1

    αβ =
    c
    = 6
    a

    Now, we are to form an equation whose roots are
    1
    ,
    1
    .
    α
    β
    So the required equation is
    x2 − (sum of roots)x + (Product of roots) = 0
    x2
    1
    +
    1
    x +
    1
    .
    1
    = 0
    αβαβ
    x2 -
    α + β
    x +
    1
    = 0
    αβαβ

    x2 -
    5
    x +
    1
    = 0
    6
    6

    6x2 - 5x + 1 = 0
    Thus , required equation is 6x2 - 5x + 1 = 0 .



  1. Consider the equation px2 + qx + r = 0, where p, q, r are real. The roots are equal in magnitude but opposite in sign when :









  1. View Hint View Answer Discuss in Forum

    As per the given above question , we can say that
    Let, the roots be α and −α. Then, sum of roots = 0 Also, roots being not equal, discriminant ≠ 0

    q
    = 0 and q2 - 4pr ≠ 0
    p

    Correct Option: D

    As per the given above question , we can say that
    Let, the roots be α and −α. Then, sum of roots = 0 Also, roots being not equal, discriminant ≠ 0

    q
    = 0 and q2 - 4pr ≠ 0
    p
    ⟺ q = 0 and pr ≠ 0.


  1. The roots of the equation 4x - 3 × 2x × 22 + 32 = 0 would include :









  1. View Hint View Answer Discuss in Forum

    According to question , we have
    Given equation is :- 22x - 3 × 2x × 22 + 32 = 0
    ⇒ 22x - 12 × 2x + 32 = 0
    ⇒ y2 - 12y + 32 = 0, where 2x = y

    Correct Option: D

    According to question , we have
    Given equation is :- 22x - 3 × 2x × 22 + 32 = 0
    ⇒ 22x - 12 × 2x + 32 = 0
    ⇒ y2 - 12y + 32 = 0, where 2x = y
    ⇒ ( y - 8 ) ( y - 4 ) = 0
    ⇒ y = 8, y = 4
    ∴ 2x = 8 or, 2x = 4
    ⇒ 2x = 23 or, 2x = 22
    ⇒ x = 3 or, x = 2.
    Therefore , the roots of the equation are 3 and 2.



  1. 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 :









  1. View Hint View Answer Discuss in Forum

    The given equation is 3x2 + (2k + 1)x - k - 5 = 0
    Compare with ax2 + bx + c = 0, we get
    a = 3, b = 2k + 1, c = - k - 5

    ∴Sum of the roots =
    - b
    =
    - ( 2k + 1 )
    a
    3

    Correct Option: A

    The given equation is 3x2 + (2k + 1)x - k - 5 = 0
    Compare with ax2 + bx + c = 0, we get
    a = 3, b = 2k + 1, c = - k - 5

    ∴Sum of the roots =
    - b
    =
    - ( 2k + 1 )
    a
    3

    and Product of the roots =
    c
    =
    - k - 5
    =
    - ( k + 5 )
    a
    3
    3
    According to question ,
    ∵ Sum of the roots = Product of the roots
    - ( 2k + 1 )
    = -
    ( k + 5 )
    3
    3
    ⇒ 2k + 1 = k + 5
    ⇒ 2k - k = 5 - 1
    ⇒ k = 4.
    Therefore , the value of k is 4 .