Chapter 14 Trigonometric Graphs, Identities, and Equations - 14.7 Apply Double-Angle and Half-Angle Formulas - 14.7 Exercises - Skill Practice - Page 960: 30

The result has been verified.

Use the Identity $ 2 \cos^2 \theta =1+ \cos 2 \theta$ Use the correct identity $\cos 2 \theta=1+\cos 2 \theta$ or, $2 \cos^2 \theta=1+ 2 \cos^2 \theta-1$ $2 \cos^2 \theta=2 \cos^2 \theta$ Hence, the result has been verified.