Chapter 9 - Trigonometric Identities, Models, and Complex Numbers - 9.5 Sums with Different Periods and Acoustic Beats - Exercises and Problems for Section 9.5 - Exercises and Problems - Page 385: 2

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

Finding the exact value using the Laws of Trigonometry, we obtain: $$2\cos \left(45^{\circ \:}\right)\cos \left(30^{\circ \:}\right) \\ 2\cdot \frac{\sqrt{2}}{2}\cdot \frac{\sqrt{3}}{2} \\ \sqrt{\frac{3}{2}}$$