hi

A1 if you check x=pi/2 + k*pi you will see that those aren't the answers to the equation,so you can divide by cos(x) without the fear of dividing by zero.

A2 if you divide by sin(x) you will get an equation in terms of cot(x),so an equation with terms in tan(x) might be better for solving.anyway if you deal with cot(x) as well as with tan(x) than you can also divide by sin(x).

PS never,i mean never divide by zero.you can make that mistake only once.