$1.37, 2.30, 3.98, 4.91\ rad$
Work Step by Step
Step 1. Graph the function $f(x)=15cos^2x+7cos(x)-2$ as shown in the figure. Step 2. Find the x-intercepts within $[0,2\pi)$ which are the solutions: $1.37, 2.30, 3.98, 4.91\ rad$
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