# Chapter 7 - Section 7.3 - Double-Angle, Half-Angle, and Product-Sum Formulas - 7.3 Exercises - Page 561: 28

$\frac{1}{2}\sqrt{2-\sqrt{3}}$

#### Work Step by Step

Use the half-angle formula, $\sin\frac{u}{2}=\pm\sqrt{\frac{1-\cos u}{2}}$. Note that $\frac{11\pi}{12}$ is in Quadrant II, where sine is positive, so we take the positive square root. $\sin \frac{11\pi}{12}$ $=\sin \frac{\frac{11\pi}{6}}{2}$ $=\sqrt{\frac{1-\cos \frac{11\pi}{6}}{2}}$ $=\sqrt{\frac{1-\frac{\sqrt{3}}{2}}{2}}$ $=\sqrt{\frac{(1-\frac{\sqrt{3}}{2})*2}{2*2}}$ $=\sqrt{\frac{2-\sqrt{3}}{4}}$ $=\frac{\sqrt{2-\sqrt{3}}}{\sqrt{4}}$ $=\frac{1}{2}\sqrt{2-\sqrt{3}}$

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