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A quadratic equation is given by x2 + (2k+2)x + 2k+5 = 0. Part (a) asks for values of k where the roots are equal. Part (b) asks for a new quadratic equation with integral coefficients for k > 0, whos

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3 parts
a

k=2,−2k=2, -2

b

x2−6x+9=0x^2 - 6x + 9 = 0

b(ii)

−1<x≤2-1 < x \le 2

Step-by-step solution

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Here's the solution to question 2:

Part i

Given the quadratic equation x2+(2k+2)x+2k+5=0x^2 + (2k+2)x + 2k+5 = 0.

Let the roots be α\alpha and β\beta.
From the equation, we have:
Sum of roots: α+β=−(2k+2)\alpha + \beta = -(2k+2)
Product of roots: αβ=2k+5\alpha \beta = 2k+5

Part a

k=2,−2k=2, -2

Find the values of the constant kk for which α=β\alpha = \beta.

If the roots are equal, the discriminant (Δ\Delta) must be zero.
The discriminant is Δ=b2−4ac\Delta = b^2 - 4ac.
Here, a=1a=1, b=(2k+2)b=(2k+2), c=(2k+5)c=(2k+5).

Δ=(2k+2)2−4(1)(2k+5)=0\Delta = (2k+2)^2 - 4(1)(2k+5) = 0 4k2+8k+4−8k−20=04k^2 + 8k + 4 - 8k - 20 = 0 4k2−16=04k^2 - 16 = 0 4k2=164k^2 = 16 k2=4k^2 = 4 k=±4k = \pm \sqrt{4} k=±2k = \pm 2

The values of kk are 2 and −2-2.

k=2,−2\boxed{k=2, -2}

Part b

x2−6x+9=0x^2 - 6x + 9 = 0

For k>0k > 0, find the quadratic equation with integral coefficients, whose roots are 2α+αβ2\alpha + \alpha\beta and 2β+αβ2\beta + \alpha\beta.

Since k>0k > 0, we use k=2k=2.
Substitute k=2k=2 into the sum and product of roots for the original equation:

α+β=−(2(2)+2)=−(4+2)=−6\alpha + \beta = -(2(2)+2) = -(4+2) = -6 αβ=2(2)+5=4+5=9\alpha \beta = 2(2)+5 = 4+5 = 9

Let the new roots be r1=2α+αβr_1 = 2\alpha + \alpha\beta and r2=2β+αβr_2 = 2\beta + \alpha\beta.

  1. Calculate the sum of the new roots (r1+r2r_1 + r_2).

    r1+r2=(2α+αβ)+(2β+αβ)r_1 + r_2 = (2\alpha + \alpha\beta) + (2\beta + \alpha\beta) r1+r2=2α+2β+2αβr_1 + r_2 = 2\alpha + 2\beta + 2\alpha\beta r1+r2=2(α+β)+2αβr_1 + r_2 = 2(\alpha + \beta) + 2\alpha\beta

    Substitute the values of α+β\alpha+\beta and αβ\alpha\beta:

    r1+r2=2(−6)+2(9)r_1 + r_2 = 2(-6) + 2(9) r1+r2=−12+18r_1 + r_2 = -12 + 18 r1+r2=6r_1 + r_2 = 6
  2. Calculate the product of the new roots (r1r2r_1 r_2).

    r1r2=(2α+αβ)(2β+αβ)r_1 r_2 = (2\alpha + \alpha\beta)(2\beta + \alpha\beta)

    Factor out α\alpha from the first term and β\beta from the second term:

    r1r2=α(2+β)⋅β(2+α)r_1 r_2 = \alpha(2+\beta) \cdot \beta(2+\alpha) r1r2=αβ(2+β)(2+α)r_1 r_2 = \alpha\beta (2+\beta)(2+\alpha) r1r2=αβ(4+2α+2β+αβ)r_1 r_2 = \alpha\beta (4 + 2\alpha + 2\beta + \alpha\beta) r1r2=αβ(4+2(α+β)+αβ)r_1 r_2 = \alpha\beta (4 + 2(\alpha + \beta) + \alpha\beta)

    Substitute the values of α+β\alpha+\beta and αβ\alpha\beta:

    r1r2=9(4+2(−6)+9)r_1 r_2 = 9 (4 + 2(-6) + 9) r1r2=9(4−12+9)r_1 r_2 = 9 (4 - 12 + 9) r1r2=9(1)r_1 r_2 = 9 (1) r1r2=9r_1 r_2 = 9
  3. Form the quadratic equation.

    A quadratic equation with roots r1r_1 and r2r_2 is given by x2−(r1+r2)x+r1r2=0x^2 - (r_1+r_2)x + r_1r_2 = 0.

    x2−(6)x+9=0x^2 - (6)x + 9 = 0 x2−6x+9=0x^2 - 6x + 9 = 0 x2−6x+9=0\boxed{x^2 - 6x + 9 = 0}

Part b(ii)

−1<x≤2-1 < x \le 2

Find the range of values of xx for which 2−xx+1≥0\frac{2-x}{x+1} \ge 0.

  1. Find the critical points.

    The numerator is zero when 2−x=0  ⟹  x=22-x=0 \implies x=2.
    The denominator is zero when x+1=0  ⟹  x=−1x+1=0 \implies x=-1.
    These points divide the number line into three intervals: (−∞,−1)(-\infty, -1), (−1,2)(-1, 2), and (2,∞)(2, \infty).

  2. Test a value in each interval.

    • For x<−1x < -1 (e.g., x=−2x=-2): 2−(−2)−2+1=4−1=−4\frac{2-(-2)}{-2+1} = \frac{4}{-1} = -4. This is <0< 0.
    • For −1<x<2-1 < x < 2 (e.g., x=0x=0): 2−00+1=21=2\frac{2-0}{0+1} = \frac{2}{1} = 2. This is ≥0\ge 0.
    • For x>2x > 2 (e.g., x=3x=3): 2−33+1=−14\frac{2-3}{3+1} = \frac{-1}{4}. This is <0< 0.
  3. Determine the solution based on the inequality.

    We need 2−xx+1≥0\frac{2-x}{x+1} \ge 0. This is satisfied when −1<x<2-1 < x < 2.
    Since the inequality includes "equal to" (≥\ge), the value x=2x=2 (where the numerator is zero) is included in the solution.
    The value x=−1x=-1 (where the denominator is zero) makes the expression undefined, so it must be excluded.
    Therefore, the range of values for xx is −1<x≤2-1 < x \le 2.

    −1<x≤2\boxed{-1 < x \le 2}
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