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

Mathematics

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2 parts
a

α3+β3=−827\alpha^3 + \beta^3 = -\frac{8}{27}

b

4x2−4x+9=04x^2 - 4x + 9 = 0

Step-by-step solution

6 steps

Here's the solution for question 1(i):

Part a· 3 steps

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

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}.
In this case, a=3a=3, b=−4b=-4, c=2c=2.

  1. Find the sum and product of the roots.

    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.

    We know that α3+β3=(α+β)(α2−αβ+β2)\alpha^3 + \beta^3 = (\alpha + \beta)(\alpha^2 - \alpha\beta + \beta^2).
    Also, 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)[169−2]\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 that α3+β3=−827\boxed{\alpha^3 + \beta^3 = -\frac{8}{27}}.

Part b

4x2−4x+9=04x^2 - 4x + 9 = 0

We need to 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 p=1α2p = \frac{1}{\alpha^2} and q=1β2q = \frac{1}{\beta^2}.
The general form of a quadratic equation is x2−(p+q)x+pq=0x^2 - (p+q)x + pq = 0.

  1. Calculate the sum of the new roots, p+qp+q.

    p+q=1α2+1β2=β2+α2(αβ)2p+q = \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

    Using values from part a): α+β=43\alpha + \beta = \frac{4}{3} and αβ=23\alpha\beta = \frac{2}{3}.

    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 substitute this into the sum of new roots:

    p+q=49(23)2=4949=1p+q = \frac{\frac{4}{9}}{\left(\frac{2}{3}\right)^2} = \frac{\frac{4}{9}}{\frac{4}{9}} = 1
  2. Calculate the product of the new roots, pqpq.

    pq=(1α2)(1β2)=1(αβ)2pq = \left(\frac{1}{\alpha^2}\right)\left(\frac{1}{\beta^2}\right) = \frac{1}{(\alpha\beta)^2} pq=1(23)2=149=94pq = \frac{1}{\left(\frac{2}{3}\right)^2} = \frac{1}{\frac{4}{9}} = \frac{9}{4}
  3. Form the new quadratic equation.

    x2−(p+q)x+pq=0x^2 - (p+q)x + pq = 0 x2−(1)x+94=0x^2 - (1)x + \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 whose roots are 1α2\frac{1}{\alpha^2} and 1β2\frac{1}{\beta^2} is 4x2−4x+9=0\boxed{4x^2 - 4x + 9 = 0}.

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