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
Question 4
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
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Answer
To find α2β3+α3β2+αβ2, 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.
Step 2
Find $\alpha^2 + \beta^2 + \gamma^2$
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Answer
Using the identity α2+β2+γ2=(alpha+β+γ)2−2(αβ+βheta+θα),
drawing from Vieta's results obtained in the previous step:
α2+β2+γ2=(−37)2−2(311)=949−322=949−66=9−17.
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=9−17, 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) are real.}
Step 4
Prove that $\angle AHE = \angle DCE$
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Answer
To prove that ∠AHE=∠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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Answer
From the equality of angles ∠AHE=∠DCE, we can use the properties of cyclic quadrilaterals: since these segments connect at H where perpendiculars meet, we conclude AH=AL.
Step 6
State a similar result for triangle AMH
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By symmetry and properties of the isosceles formed by A, M, and the intersection points, we state that AM=AH.
Step 7
Show that the length of arc BKC is half the length of arc MKL
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Since ∠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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Using the equation of PQ: x0y−y0=b2y0, we substitute the coordinates of point T relative to the ellipse, showing that it satisfies the directrix condition x=−ea2, confirming T lies on the directrix.
Step 9
What is the value of the ratio PS/ST?
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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:
STPS=QSSP.
Step 10
Show that $\angle ZPTQ$ is less than a right angle
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Since angles in opposite segments of a cyclic figure yield acute angles, we can prove that ∠ZPTQ<90∘ 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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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(e1−1).