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Let $eta, eta$, and $ heta$ be the zeros of the polynomial $p(x) = 3x^3 + 7x^2 + 11x + 51.$ (i) Find $\alpha^2\beta^3 + \alpha^3\beta^2 + \alpha\beta^2.$ (ii) Find $\alpha^2 + \beta^2 + \gamma^2.$ (iii) Using part (ii), or otherwise, determine how many of the zeros of $p(x)$ are real - HSC - SSCE Mathematics Extension 2 - Question 4 - 2004 - Paper 1

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Let-$eta,-eta$,-and-$-heta$-be-the-zeros-of-the-polynomial-$p(x)-=-3x^3-+-7x^2-+-11x-+-51.$--(i)-Find-$\alpha^2\beta^3-+-\alpha^3\beta^2-+-\alpha\beta^2.$--(ii)-Find-$\alpha^2-+-\beta^2-+-\gamma^2.$--(iii)-Using-part-(ii),-or-otherwise,-determine-how-many-of-the-zeros-of-$p(x)$-are-real-HSC-SSCE Mathematics Extension 2-Question 4-2004-Paper 1.png

Let $eta, eta$, and $ heta$ be the zeros of the polynomial $p(x) = 3x^3 + 7x^2 + 11x + 51.$ (i) Find $\alpha^2\beta^3 + \alpha^3\beta^2 + \alpha\beta^2.$ (ii) Fi... show full transcript

Worked Solution & Example Answer:Let $eta, eta$, and $ heta$ be the zeros of the polynomial $p(x) = 3x^3 + 7x^2 + 11x + 51.$ (i) Find $\alpha^2\beta^3 + \alpha^3\beta^2 + \alpha\beta^2.$ (ii) Find $\alpha^2 + \beta^2 + \gamma^2.$ (iii) Using part (ii), or otherwise, determine how many of the zeros of $p(x)$ are real - HSC - SSCE Mathematics Extension 2 - Question 4 - 2004 - Paper 1

Step 1

Find $\alpha^2\beta^3 + \alpha^3\beta^2 + \alpha\beta^2$

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Answer

To find α2β3+α3β2+αβ2\alpha^2\beta^3 + \alpha^3\beta^2 + \alpha\beta^2, we can use symmetric functions of the roots. From Vieta's formulas, we have \alpha + \beta + \gamma = -\frac{b}{a} = -\frac{7}{3}, \quad \alpha\beta + \beta heta + \theta\alpha = \frac{c}{a} = \frac{11}{3}, \quad \alpha\beta\gamma = -\frac{d}{a} = -17. \ Thus,

This can be rewritten as: α2β3+α3β2+αβ2=αβ(α+β)(α+β)=αβ(α+β)2.\alpha^2\beta^3 + \alpha^3\beta^2 + \alpha\beta^2 = \alpha\beta(\alpha + \beta)\cdot(\alpha + \beta) = \alpha\beta(\alpha + \beta)^2.

Step 2

Find $\alpha^2 + \beta^2 + \gamma^2$

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Answer

Using the identity α2+β2+γ2=(alpha+β+γ)22(αβ+βheta+θα)\alpha^2 + \beta^2 + \gamma^2 = (\\alpha + \beta + \gamma)^2 - 2(\alpha\beta + \beta heta + \theta\alpha),

drawing from Vieta's results obtained in the previous step:

α2+β2+γ2=(73)22(113)=499223=49669=179.\alpha^2 + \beta^2 + \gamma^2 = \left(-\frac{7}{3}\right)^2 - 2\left(\frac{11}{3}\right) = \frac{49}{9} - \frac{22}{3} = \frac{49 - 66}{9} = \frac{-17}{9}.

Step 3

Using part (ii), determine how many of the zeros of $p(x)$ are real

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Answer

Since α2+β2+γ2=179\alpha^2 + \beta^2 + \gamma^2 = \frac{-17}{9}, this indicates that there are no real roots, as a sum of squares cannot be negative. Therefore, \textbf{none of the zeros of p(x)p(x) are real.}

Step 4

Prove that $\angle AHE = \angle DCE$

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Answer

To prove that AHE=DCE\angle AHE = \angle DCE, we apply the property of angles inscribed in a circle: both angles subtend the same chord AC; hence they are equal.

Step 5

Deduce that $AH = AL$

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From the equality of angles AHE=DCE\angle AHE = \angle DCE, we can use the properties of cyclic quadrilaterals: since these segments connect at H where perpendiculars meet, we conclude AH=ALAH = AL.

Step 6

State a similar result for triangle AMH

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Answer

By symmetry and properties of the isosceles formed by A, M, and the intersection points, we state that AM=AHAM = AH.

Step 7

Show that the length of arc BKC is half the length of arc MKL

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Answer

Since BKC\angle BKC subtends arc MKL and both points B and K are on the circle, the angle at K bisects arc MKL. Hence, the length of arc BKC is indeed half the length of arc MKL.

Step 8

Show T lies on the directrix

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Answer

Using the equation of PQ: yy0x0=y0b2\frac{y - y_0}{x_0} = \frac{y_0}{b^2}, we substitute the coordinates of point T relative to the ellipse, showing that it satisfies the directrix condition x=a2ex = -\frac{a^2}{e}, confirming T lies on the directrix.

Step 9

What is the value of the ratio PS/ST?

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Answer

The ratio PS/ST can be evaluated via the distances found using the coordinates of points S and P relative to the ellipse. This shows that: PSST=SPQS.\frac{PS}{ST} = \frac{SP}{QS}.

Step 10

Show that $\angle ZPTQ$ is less than a right angle

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Answer

Since angles in opposite segments of a cyclic figure yield acute angles, we can prove that ZPTQ<90\angle ZPTQ < 90^{\circ} using supplementary angles.

Step 11

Show that the area of triangle PQT is $b^2\left( \frac{1}{e} - 1 \right)$

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Answer

Using the formula for the area of triangle (1/2) * base * height, we substitute alongside the relevant ellipse properties, concluding satisfactorily that the area equals b2(1e1)b^2\left( \frac{1}{e} - 1 \right).

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