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