Chapter 5: Problem 35
Use the previous problem to show that in every triangle, the sum of the lengths of any two sides is greater than the length of the third side.
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Chapter 5: Problem 35
Use the previous problem to show that in every triangle, the sum of the lengths of any two sides is greater than the length of the third side.
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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 \(\left(-\frac{\pi}{2}, 0\right) .\) $$\cos (u-v)$$
Show that $$\cos x-\cos y=2 \sin \frac{x+y}{2} \sin \frac{y-x}{2}$$ for all \(x, y\).
Find an exact expression for \(\sin 15^{\circ}\).
Find an exact expression for \(\sin \frac{\pi}{24}\).
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.]
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