Here's the problem: tan^2x-3tanx-4=0, x [0, 3pi]

What I've worked out so far:

(tanx+1)(tanx-4)=0

tan(x)=-1, tan(x)=4

arctan(-1)=x, arctan(4)=x

-0.7853982=x, 1.325818=x

I'm aware the period is 360 degrees... do I simply add 360 to both solutions and then check to see which ones are correct? How do I use the "tangent is positive in the first and fourth quadrants" to solve?