Be careful with radians versus degrees there. Which mode was your calculator in?
Here's the problem: tan^2x-3tanx-4=0, x [0, 3pi]
What I've worked out so far:
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?