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Given equation: 3x² − 4x + 2 = 0.

Mathematics

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1. (i) a) Given that the roots of the equation 3x2−4x+2=03x^2 - 4x + 2 = 0 are α\alpha and β\beta. Show that α3+β3=−827\alpha^3 + \beta^3 = -\frac{8}{27}.

  1. Identify the coefficients and find the sum and product of roots.

    For a quadratic equation ax2+bx+c=0ax^2 + bx + c = 0, the sum of roots is α+β=−ba\alpha + \beta = -\frac{b}{a} and the product of roots is αβ=ca\alpha \beta = \frac{c}{a}.
    Given equation: 3x2−4x+2=03x^2 - 4x + 2 = 0.
    Here, a=3a=3, b=−4b=-4, c=2c=2.
    Sum of roots:

    α+β=−−43=43\alpha + \beta = -\frac{-4}{3} = \frac{4}{3}

    Product of roots:

    αβ=23\alpha \beta = \frac{2}{3}
  2. Use the identity for α3+β3\alpha^3 + \beta^3.

    The identity for the sum of cubes is α3+β3=(α+β)(α2−αβ+β2)\alpha^3 + \beta^3 = (\alpha + \beta)(\alpha^2 - \alpha \beta + \beta^2).
    We can express α2+β2\alpha^2 + \beta^2 in terms of α+β\alpha + \beta and αβ\alpha \beta: α2+β2=(α+β)2−2αβ\alpha^2 + \beta^2 = (\alpha + \beta)^2 - 2\alpha \beta.
    Substitute this into the identity:

    α3+β3=(α+β)((α+β)2−2αβ−αβ)\alpha^3 + \beta^3 = (\alpha + \beta)((\alpha + \beta)^2 - 2\alpha \beta - \alpha \beta) α3+β3=(α+β)((α+β)2−3αβ)\alpha^3 + \beta^3 = (\alpha + \beta)((\alpha + \beta)^2 - 3\alpha \beta)
  3. Substitute the values of α+β\alpha + \beta and αβ\alpha \beta.

    α3+β3=(43)((43)2−3(23))\alpha^3 + \beta^3 = \left(\frac{4}{3}\right)\left(\left(\frac{4}{3}\right)^2 - 3\left(\frac{2}{3}\right)\right) α3+β3=(43)(169−63)\alpha^3 + \beta^3 = \left(\frac{4}{3}\right)\left(\frac{16}{9} - \frac{6}{3}\right) α3+β3=(43)(169−189)\alpha^3 + \beta^3 = \left(\frac{4}{3}\right)\left(\frac{16}{9} - \frac{18}{9}\right) α3+β3=(43)(−29)\alpha^3 + \beta^3 = \left(\frac{4}{3}\right)\left(-\frac{2}{9}\right) α3+β3=−827\alpha^3 + \beta^3 = -\frac{8}{27}

    This shows the required result.

    1. (i) b) Hence, find the equation with integral coefficients whose roots are 1α3\frac{1}{\alpha^3} and 1β3\frac{1}{\beta^3}.

  4. Define the new roots and calculate their sum.

    Let the new roots be p=1α3p = \frac{1}{\alpha^3} and q=1β3q = \frac{1}{\beta^3}.
    Sum of new roots:

    p+q=1α3+1β3=β3+α3α3β3p + q = \frac{1}{\alpha^3} + \frac{1}{\beta^3} = \frac{\beta^3 + \alpha^3}{\alpha^3 \beta^3}

    From part (a), we know α3+β3=−827\alpha^3 + \beta^3 = -\frac{8}{27}.
    Also, α3β3=(αβ)3\alpha^3 \beta^3 = (\alpha \beta)^3. Since αβ=23\alpha \beta = \frac{2}{3}:

    (αβ)3=(23)3=827(\alpha \beta)^3 = \left(\frac{2}{3}\right)^3 = \frac{8}{27}

    Now, substitute these values into the sum of new roots:

    p+q=−827827=−1p + q = \frac{-\frac{8}{27}}{\frac{8}{27}} = -1
  5. Calculate the product of the new roots.

    pq=(1α3)(1β3)=1α3β3=1(αβ)3pq = \left(\frac{1}{\alpha^3}\right)\left(\frac{1}{\beta^3}\right) = \frac{1}{\alpha^3 \beta^3} = \frac{1}{(\alpha \beta)^3} pq=1827=278pq = \frac{1}{\frac{8}{27}} = \frac{27}{8}
  6. Form the quadratic equation with integral coefficients.

    The general form of a quadratic equation is x2−(sum of roots)x+(product of roots)=0x^2 - (\text{sum of roots})x + (\text{product of roots}) = 0.

    x2−(−1)x+278=0x^2 - (-1)x + \frac{27}{8} = 0 x2+x+278=0x^2 + x + \frac{27}{8} = 0

    To obtain integral coefficients, multiply the entire equation by 8:

    8(x2+x+278)=8(0)8(x^2 + x + \frac{27}{8}) = 8(0) 8x2+8x+27=0\boxed{8x^2 + 8x + 27 = 0}

    1. (iii) Find the set of real values of xx for which ∣x+3x−5∣=x+3x−5\left|\frac{x+3}{x-5}\right| = \frac{x+3}{x-5}.

  7. Understand the property of absolute value.

    The equation ∣A∣=A|A| = A holds true if and only if A≥0A \ge 0.
    Therefore, we need to find the values of xx for which x+3x−5≥0\frac{x+3}{x-5} \ge 0.

  8. Find the critical points.

    The critical points are the values of xx where the numerator or denominator is zero.
    Numerator: x+3=0  ⟹  x=−3x+3 = 0 \implies x = -3.
    Denominator: x−5=0  ⟹  x=5x-5 = 0 \implies x = 5.
    These points divide the number line into three intervals: (−∞,−3)(-\infty, -3), (−3,5)(-3, 5), and (5,∞)(5, \infty).

  9. Test each interval.

    • For x<−3x < -3 (e.g., x=−4x = -4): −4+3−4−5=−1−9=19\frac{-4+3}{-4-5} = \frac{-1}{-9} = \frac{1}{9}. This is positive, so the inequality holds. Since the inequality is ≥0\ge 0, x=−3x=-3 is included (as 0−8=0\frac{0}{-8}=0). So, x≤−3x \le -3 is part of the solution.

    • For −3<x<5-3 < x < 5 (e.g., x=0x = 0): 0+30−5=3−5=−35\frac{0+3}{0-5} = \frac{3}{-5} = -\frac{3}{5}. This is negative, so the inequality does not hold.

    • For x>5x > 5 (e.g., x=6x = 6): 6+36−5=91=9\frac{6+3}{6-5} = \frac{9}{1} = 9. This is positive, so the inequality holds. Note that x=5x=5 is excluded because it makes the denominator zero, which is undefined.

  10. Combine the valid intervals.

    The set of real values of xx for which the inequality holds is x≤−3x \le -3 or x>5x > 5.
    In set notation:

    {x∈R∣x≤−3 or x>5}\boxed{\{x \in \mathbb{R} \mid x \le -3 \text{ or } x > 5\}}
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