Math Help - Trigonometric equations

1. Trigonometric equations

The sum of the roots of the equation:

belonging to the interval $[0;2\pi]$ is ?

2. Does "tgx" mean "tan(x)"? What does "sen" mean? Does "2x" mean "an argument of 2x", or "squared, of x"?

What have you tried so far? Where are you stuck?

Thank you!