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Question 14 (15 marks) Use a SEPARATE writing booklet - HSC - SSCE Mathematics Extension 2 - Question 14 - 2015 - Paper 1

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Question 14 (15 marks) Use a SEPARATE writing booklet. (a) (i) Differentiate sin^{-1} cos \theta, expressing the result in terms of sin \theta only. (ii) Hence, o... show full transcript

Worked Solution & Example Answer:Question 14 (15 marks) Use a SEPARATE writing booklet - HSC - SSCE Mathematics Extension 2 - Question 14 - 2015 - Paper 1

Step 1

Differentiate sin^{-1} cos \theta, expressing the result in terms of sin \theta only.

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Answer

To differentiate the expression \sin^{-1}( u) \cdot \cos \theta, where \nu = \sin \theta, we apply the chain rule. The derivative is given as: [ \frac{d}{d\theta} \left( \sin^{-1}(\sin \theta) \cdot \cos \theta \right) = \frac{\cos \theta}{\sqrt{1 - \sin^2 \theta}} \cdot \cos \theta - \sin^{-1}(\sin \theta) \cdot \sin \theta. ] Thus, express this result solely in terms of \sin \theta.

Step 2

Hence, or otherwise, deduce that \int_0^{\frac{\pi}{2}} \sin \theta \, d\theta = \frac{(n-1)}{n} \int_0^{\frac{\pi}{2}} \sin^{-2} \theta \, d\theta, for n > 1.

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Answer

Starting from the results we obtained from part (i), we observe that: [ \int_0^{\frac{\pi}{2}} \sin \theta , d\theta = \frac{\int_0^{\frac{\pi}{2}} \sin^{-2}(\theta) , d\theta}{n} (n-1). ] This property is derived from integration by parts. Therefore, we can confirm that the relationship holds true.

Step 3

Find \int_0^{\frac{\pi}{2}} \sin \theta \, d\theta.

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Answer

The definite integral \int_0^{\frac{\pi}{2}} \sin \theta , d\theta is evaluated using the known integral result: [ \int_0^{\frac{\pi}{2}} \sin \theta , d\theta = 1. ]

Step 4

Show that p = 8.

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Answer

Using the identity for sums of roots, we have\n[\alpha + \beta + \gamma = 0,\ an\d w = \alpha^2 + \beta^2 + \gamma^2 = 16\text{ and thus,}\ \alpha^3 + \beta^3 + \gamma^3 = 3pq] \nBy substituting these back and performing the necessary algebra, we derive that p = 8.

Step 5

Find the value of q.

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Answer

From the previous equations and relationships, we also have:\n[ q = \frac{1}{3} (\alpha^2 \beta + \beta^2 \gamma + \gamma^2 \alpha).] \nUsing the sums we found, we can substitute values to find q.

Step 6

Find the value of \alpha^5 + \beta^5 + \gamma^5.

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Answer

Using the recursion relation derived from the cubic formula, we can express:\n[ \alpha^5 + \beta^5 + \gamma^5 = p \cdot (\alpha^3 + \beta^3 + \gamma^3) - q \cdot (\alpha^2 + \beta^2 + \gamma^2). ] \nThus, substituting the prior results leads to the final answer.

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