2.
設\( 0 \le x \le 2 \pi \)，求\( tan^2x-9tanx+1=0 \)之各根總和為多少？

112.8.22補充
若\(0\le x \le 2\pi\)，則滿足\(tan^2 x-9tanx+1=0\)的所有\(x\)值之和為　　　。
(111高中數學能力競賽　第一區(花蓮高中)筆試二試題，https://math.pro/db/thread-3782-1-1.html)

Find the sum of the roots of \( tan^2x-9tanx+1=0 \) that are between \( x=0 \) and \( x=2 \pi \) radians.
(A)\( \displaystyle \frac{\pi}{2} \)　(B)\( \pi \)　(C)\( \displaystyle \frac{3\pi}{2} \)　(D)\( 3\pi \)　(E)\( 4\pi \)
(1989AHSME，https://artofproblemsolving.com/ ... Problems/Problem_28)