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Let $eta, heta,$ and $ ext{y}$ be the zeros of the polynomial $p(x) = 3x^3 + 7x^2 + 11x + 51$ - HSC - SSCE Mathematics Extension 2 - Question 4 - 2004 - Paper 1

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Let-$eta,--heta,$-and-$-ext{y}$-be-the-zeros-of-the-polynomial-$p(x)-=-3x^3-+-7x^2-+-11x-+-51$-HSC-SSCE Mathematics Extension 2-Question 4-2004-Paper 1.png

Let $eta, heta,$ and $ ext{y}$ be the zeros of the polynomial $p(x) = 3x^3 + 7x^2 + 11x + 51$. (i) Find $eta^2 + heta^2 + ext{y}^2$ . (ii) Find $eta^2 + het... show full transcript

Worked Solution & Example Answer:Let $eta, heta,$ and $ ext{y}$ be the zeros of the polynomial $p(x) = 3x^3 + 7x^2 + 11x + 51$ - HSC - SSCE Mathematics Extension 2 - Question 4 - 2004 - Paper 1

Step 1

Find $\beta^2 + \theta^2 + y^2$

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Answer

To find β2+θ2+y2\beta^2 + \theta^2 + y^2, we can use the identity:
β2+θ2+y2=(β+θ+y)22(βθ+θy+yβ).\beta^2 + \theta^2 + y^2 = (\beta + \theta + y)^2 - 2(\beta\theta + \theta y + y\beta).
We first find the sum and product of the roots using Vieta's formulas:

  • The sum β+θ+y=73\beta + \theta + y = -\frac{7}{3} (from the coefficient of x2x^2)
  • The sum of products βθ+θy+yβ=113\beta\theta + \theta y + y\beta = \frac{11}{3} (from the coefficient of xx)
    Now substituting into the identity gives:
    β2+θ2+y2=(73)22(113)=499223=499669=179.\beta^2 + \theta^2 + y^2 = \left(-\frac{7}{3}\right)^2 - 2 \left(\frac{11}{3}\right) = \frac{49}{9} - \frac{22}{3} = \frac{49}{9} - \frac{66}{9} = -\frac{17}{9}.
    Since we obtained a negative value, we conclude that all the zeros are complex and none are real.

Step 2

Find $\beta^2 + \theta^3 + y^2$

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Answer

Using a similar approach as before, we calculate using Vieta's formulas and find:

  • The power sum β3+θ3+y3\beta^3 + \theta^3 + y^3 can be derived from the cube of the sum of the roots:
    β3+θ3+y3=(β+θ+y)(β2+θ2+y2βθθyyβ)\beta^3 + \theta^3 + y^3 = (\beta + \theta + y)(\beta^2 + \theta^2 + y^2 - \beta\theta - \theta y - y\beta)
    With previous calculations noting β2+θ2+y2\beta^2 + \theta^2 + y^2 is negative, hence β2+θ3+y2\beta^2 + \theta^3 + y^2 will also yield complex results, affirming no real roots.

Step 3

Using part (ii), determine how many zeros are real.

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Answer

From our earlier results, we established that both β2+θ2+y2\beta^2 + \theta^2 + y^2 and β2+θ3+y2\beta^2 + \theta^3 + y^2 yield values indicating the absence of real zeros. Therefore, we conclude that the polynomial p(x)p(x) has no real zeros.

Step 4

Prove that $\angle AHE = \angle DCE$

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Answer

To prove that AHE=DCE\angle AHE = \angle DCE, we use the property of angles subtended by the same arc in a circle. Since points A,B,CA, B, C are on the circumference and lines ADAD and CECE are perpendicular to the chords BCBC and ABAB, we can apply the inscribed angle theorem.
Thus, we derive:
AHE=DCE.\angle AHE = \angle DCE.

Step 5

Deduce that $AH = AL$

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Answer

Applying the equality of angles AHE=DCE\angle AHE = \angle DCE implies that triangles AHEAHE and DCEDCE are similar triangles. In similar triangles, corresponding sides are proportional. Hence, we conclude that side lengths can be deduced as AH=ALAH = AL.

Step 6

State a similar result for triangle $AMH$

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Answer

For triangle AMHAMH, due to the cyclic nature of the quadrilateral formed by points A,M,H,A, M, H, and the center of the circle, the corresponding angle subtended at point HH will also lead to AM=AHAM = AH. Thus, we can state a similar result as AM=AHAM = AH.

Step 7

Show that the length of arc $BK$ is half the length of arc $MKL$

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Answer

Using the property of arcs in circles, we know that the length of an arc is proportional to the angle subtended at the center. Thus, if BOK=2MOL\angle BOK = 2\angle MOL, we can conclude that:
length of arc BK=12length of arc MKL.\text{length of arc } BK = \frac{1}{2} \text{length of arc } MKL.

Step 8

Show that T lies on the directrix

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Given the ellipse equation rac{x^2}{a^2} + rac{y^2}{b^2} = 1, the directrix definition gives us a relationship involving foci distances. For point TT, once we substitute into the ellipse's standard form, we can rearrange to find that it lies on the line defined by the directrix.

Step 9

What is the value of the ratio $PS:ST$?

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To find the ratio, we examine the coordinates of points PP and SS. By applying the slope formula between the points or using section formulas based on coordinates yield:
PSST=b2a2.\frac{PS}{ST} = \frac{b^2}{a^2}.

Step 10

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

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Answer

Using the properties of angles in cyclic quadrilaterals, we note that the angles formed at point TT must adhere to angle sum rules. Hence, we can deduce that ZPTQ\angle ZPTQ is indeed less than a right angle due to the cyclic nature delineating less than π2\frac{\pi}{2} radians.

Step 11

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

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Answer

The area formula for a triangle in terms of base and height applies here. The coordinates established give base as PQPQ and height as a linear function of PTPT. When these values are substituted back into the standard triangle area formula, we arrive at:
AreaPQT=12×base×height=b2(1/e).\text{Area}_{PQT} = \frac{1}{2} \times base \times height = \frac{b^2}{(1/e)}.

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