$F(x)=3 \cdot \cos 2=\frac{\pi}{3}$
\(\boxed{0.607}\)
Step 1 :\(F(x) = 3 \cdot \cos 2x = \frac{\pi}{3}\)
Step 2 :\(\cos 2x = \frac{\pi}{9}\)
Step 3 :\(2x = \arccos \left(\frac{\pi}{9}\right)\)
Step 4 :\(x = \frac{1}{2} \arccos \left(\frac{\pi}{9}\right)\)
Step 5 :\(x \approx 0.607\)
Step 6 :\(\boxed{0.607}\)