All worksheets topics

2.7 Quadratic equations, inequalities and the discriminantIB Maths: Analysis and Approaches HL: Subtopic test

10 questions, 27 marks

IB Maths: Analysis and Approaches HL

2.7 Quadratic equations, inequalities and the discriminant

Total 27 marks

Name

Class

Date

  1. 1
    Let f(x)=2x2−5x−3f(x) = 2x^{2} - 5x - 3, x∈Rx \in \mathbb{R}.
    (a)
    Find the solutions of the equation f(x)=0f(x) = 0.
    [1 mark]
    • Ax=−12x = -\frac{1}{2} or x=3x = 3
    • Bx=12x = \frac{1}{2} or x=−3x = -3
    • Cx=−1x = -1 or x=32x = \frac{3}{2}
    • Dx=−1x = -1 or x=6x = 6
    (b)
    Find the value of the discriminant of f(x)f(x).
    [1 mark]
    • A11
    • B4949
    • C−49-49
    • D77
    (c)
    Solve the inequality f(x)<0f(x) < 0.
    [2 marks]

    Total for question 1: 4 marks

  2. 2
    Consider the equation x2+(k−2)x+4=0x^{2} + (k - 2)x + 4 = 0, where k∈Rk \in \mathbb{R}.
    (a)
    Find an expression, in terms of kk, for the discriminant of this equation.
    [1 mark]
    • Ak2−4k+20k^{2} - 4k + 20
    • Bk2−12k^{2} - 12
    • Ck2+4k−12k^{2} + 4k - 12
    • Dk2−4k−12k^{2} - 4k - 12
    (b)
    Find the values of kk for which the equation has two equal real roots.
    [1 mark]
    • Ak=6k = 6 only
    • Bk=2k = 2 or k=−6k = -6
    • Ck=−2k = -2 or k=6k = 6
    • Dk=4k = 4 or k=−4k = -4
    (c)
    Find the set of values of kk for which the equation has no real roots.
    [2 marks]

    Total for question 2: 4 marks

  3. 3
    A farmer has 40 m of fencing to make a rectangular pen against a long straight wall. The wall forms one side of the pen and the fencing forms the other three sides. Each of the two sides perpendicular to the wall has length xx metres.
    (a)
    Find the values of xx for which the area of the pen is 150 m2150\ \text{m}^{2}.
    [3 marks]
    (b)
    By considering the discriminant of a suitable quadratic equation, find the maximum possible area of the pen. Justify your answer.
    [4 marks]

    Total for question 3: 7 marks

  4. 4
    The curve CC has equation y=x2−6x+14y = x^{2} - 6x + 14. For each k∈Rk \in \mathbb{R}, the line LkL_{k} has equation y=kx+5y = kx + 5.
    (a)
    (i) Write x2−6x+14x^{2} - 6x + 14 in the form (x−h)2+q(x - h)^{2} + q, where h,q∈Zh, q \in \mathbb{Z}.
    (ii) Hence write down the coordinates of the vertex of
    CC and explain why CC does not meet the xx-axis.
    (iii) Show that the
    xx-coordinates of any points where CC and LkL_{k} meet satisfy x2−(6+k)x+9=0x^{2} - (6 + k)x + 9 = 0.
    [6 marks]
    (b)
    (i) Find the values of kk for which LkL_{k} is a tangent to CC.
    (ii) Find the set of values of
    kk for which LkL_{k} does not meet CC.
    [6 marks]

    Total for question 4: 12 marks

End of questions