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Given the quadratic equation 3x² − 4x + 2 = 0, with roots alpha and beta.

Mathematics

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Answer

\text{4x^2 - 4x + 9 = 0}

x≤−3 or x>1x \le -3 \text{ or } x > 1

Step-by-step solution

8 steps

Here's the solution to question 1:

1(i)a) Show that α3+β3=−827\alpha^3 + \beta^3 = -\frac{8}{27}

Given the quadratic equation 3x2−4x+2=03x^2 - 4x + 2 = 0, with roots α\alpha and β\beta.

  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}.
    Here, a=3a=3, b=−4b=-4, c=2c=2.

    α+β=−−43=43\alpha + \beta = -\frac{-4}{3} = \frac{4}{3} αβ=23\alpha \beta = \frac{2}{3}
  2. Use the identity for α3+β3\alpha^3 + \beta^3.

    The identity is 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)(169−2)\alpha^3 + \beta^3 = \left(\frac{4}{3}\right)\left(\frac{16}{9} - 2\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) Find the equation with integral coefficients whose roots are 1α2\frac{1}{\alpha^2} and 1β2\frac{1}{\beta^2}

    Let the new roots be r1=1α2r_1 = \frac{1}{\alpha^2} and r2=1β2r_2 = \frac{1}{\beta^2}.
    The general quadratic equation is x2−(sum of roots)x+(product of roots)=0x^2 - (\text{sum of roots})x + (\text{product of roots}) = 0.

  4. Calculate the sum of the new roots.

    S′=1α2+1β2=β2+α2(αβ)2S' = \frac{1}{\alpha^2} + \frac{1}{\beta^2} = \frac{\beta^2 + \alpha^2}{(\alpha \beta)^2}

    First, find α2+β2\alpha^2 + \beta^2:

    α2+β2=(α+β)2−2αβ\alpha^2 + \beta^2 = (\alpha + \beta)^2 - 2\alpha \beta

    Substitute the values from part (a):

    α2+β2=(43)2−2(23)=169−43=169−129=49\alpha^2 + \beta^2 = \left(\frac{4}{3}\right)^2 - 2\left(\frac{2}{3}\right) = \frac{16}{9} - \frac{4}{3} = \frac{16}{9} - \frac{12}{9} = \frac{4}{9}

    Now, calculate S′S':

    S′=49(23)2=4949=1S' = \frac{\frac{4}{9}}{\left(\frac{2}{3}\right)^2} = \frac{\frac{4}{9}}{\frac{4}{9}} = 1
  5. Calculate the product of the new roots.

    P′=(1α2)(1β2)=1(αβ)2P' = \left(\frac{1}{\alpha^2}\right)\left(\frac{1}{\beta^2}\right) = \frac{1}{(\alpha \beta)^2}

    Substitute the value of αβ\alpha \beta:

    P′=1(23)2=149=94P' = \frac{1}{\left(\frac{2}{3}\right)^2} = \frac{1}{\frac{4}{9}} = \frac{9}{4}
  6. Form the new quadratic equation.

    The equation is x2−S′x+P′=0x^2 - S'x + P' = 0.

    x2−1x+94=0x^2 - 1x + \frac{9}{4} = 0

    To obtain integral coefficients, multiply the entire equation by 4:

    4x2−4x+9=04x^2 - 4x + 9 = 0

    The equation with integral coefficients is \boxed{\text{4x^2 - 4x + 9 = 0}}.

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

    The property ∣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−1≥0\frac{x+3}{x-1} \ge 0.
    Also, the denominator cannot be zero, so x−1≠0  ⟹  x≠1x-1 \ne 0 \implies x \ne 1.

  7. Analyze the signs of the numerator and denominator.

    For the fraction to be non-negative, both numerator and denominator must have the same sign (or the numerator is zero).

    Case 1: Numerator is non-negative and denominator is positive.
    x+3≥0  ⟹  x≥−3x+3 \ge 0 \implies x \ge -3
    x−1>0  ⟹  x>1x-1 > 0 \implies x > 1
    The intersection of these conditions is x>1x > 1.

    Case 2: Numerator is non-positive and denominator is negative.
    x+3≤0  ⟹  x≤−3x+3 \le 0 \implies x \le -3
    x−1<0  ⟹  x<1x-1 < 0 \implies x < 1
    The intersection of these conditions is x≤−3x \le -3.

  8. Combine the solutions from both cases.

    The set of real values of xx is x≤−3x \le -3 or x>1x > 1.
    In interval notation, this is (−∞,−3]∪(1,∞)(-\infty, -3] \cup (1, \infty).

    The set of real values of xx is x≤−3 or x>1\boxed{x \le -3 \text{ or } x > 1}.

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