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Three different points A, B and C are chosen on a circle centred at O - HSC - SSCE Mathematics Extension 1 - Question 13 - 2022 - Paper 1

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Three different points A, B and C are chosen on a circle centred at O. Let $a = OA$, $b = OB$ and $c = OC$. Let $h = a + b + c$ and let H be the point such that $OH... show full transcript

Worked Solution & Example Answer:Three different points A, B and C are chosen on a circle centred at O - HSC - SSCE Mathematics Extension 1 - Question 13 - 2022 - Paper 1

Step 1

Show that \(\bar{BH}\) and \(\bar{CA}\) are perpendicular.

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Answer

Let the equation of the solid generated by the revolution be calculated using the integral:

[ V = \int_{0}^{\frac{\pi}{2k}} \pi((k + 1) \sin(kx))^2 dx ]

To find the volume, set:
(V = \pi^{2}) and solve for (k).

After simplifications, we find that:

[ k = 1 \text{ or } k = 2 \text{ are valid solutions.} ]

Step 2

Is \(g\) the inverse of \(f^2\)?

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Answer

To determine if (g) is the inverse of (f^2), we check if (g(f(x)) = x) holds true for all (x) in the domain of (f).

Since (f(x) = \sin(x)) and (g(x) = \arcsin(x)), we find that:

For (y = f(x) = \sin(x)):
[ g(y) = g(f(x)) = \arcsin(\sin(x)) = x \text{ iff } |x| \le 1 ]

Thus, (g) is not the inverse of (f^2) over the reals, since (f^2) is restricted to (x\ in \mathbb{R}). However, it is for a restricted domain that excludes non-invertible intervals.

Step 3

Find \(\alpha\beta + \beta\gamma + \gamma\alpha\).

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Answer

Using the identity: [ \alpha^2 + \beta^2 + \gamma^2 = 85 ],
we also know: [ P' (\alpha) + P' (\beta) + P' (\gamma) = 87 ].

From the polynomial roots, we derive: [ \alpha \beta + \beta \gamma + \gamma \alpha = p = \frac{P'}{2} = 87-85/2 \text{ leading to the value} ]

Step 4

Calculate \(P_{p}\).

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Answer

Using the normal approximation: [ P_{p} \text{ can be calculated based on } \text{mean } = 0.8 \times 16 = 12.8 \text{ and standard deviation } = \sqrt{16 \times 0.8 \times 0.2} ] We find: [ P = P(X \geq 8) \text{ using the cumulative distribution function.} ]

Step 5

Explain why the method used by the inspectors might not be valid.

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Answer

The inspectors' use of a normal approximation in a discrete distribution context may not hold due to the small sample size, which can lead to inaccuracies. Assuming a binomial distribution while approximating might ignore the variability among individual weights causing misjudgment in estimation.

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