Chapter 5: Problem 65
Find an exact expression for \(\sin \frac{\pi}{24}\).
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Chapter 5: Problem 65
Find an exact expression for \(\sin \frac{\pi}{24}\).
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Show that \(\cos 20^{\circ}\) is a zero of the polynomial \(8 x^{3}-6 x-1\) [Hint: Set \(\theta=20^{\circ}\) in the identity from the previous problem.]
Show that $$\cos x+\cos y=2 \cos \frac{x+y}{2} \cos \frac{x-y}{2}$$ for all \(x, y\). [Hint: Take \(u=\frac{x+y}{2}\) and \(v=\frac{x-y}{2}\) in the formula given by Example 5 .]
Find a formula for \(\tan \left(\theta-\frac{\pi}{2}\right)\).
Evaluate the indicated expressions assuming that $$ \begin{array}{ll} \cos x=\frac{1}{3} & \text { and } \sin y=\frac{1}{4} \\ \sin u=\frac{2}{3} & \text { and } \cos v=\frac{1}{5} \end{array} $$ Assume also that \(x\) and \(u\) are in the interval \(\left(0, \frac{\pi}{2}\right),\) that \(y\) is in the interval \(\left(\frac{\pi}{2}, \pi\right),\) and that \(v\) is in the interval \(\left(-\frac{\pi}{2}, 0\right) .\) $$\sin (x+y)$$
Show that $$\cos \frac{\pi}{32}=\frac{\sqrt{2+\sqrt{2+\sqrt{2+\sqrt{2}}}}}{2}$$ [Hint: First do Exercise 66.]
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