That's the one posted. Correct and re-write it.
As posted, it defies any ammount of head-scratching.
If that is
tan^2(theta) = 1/3, then,
Take the square root of both sides,
tan(theta) = +,- 1 / sqrt(3)
Plus or minus tan value. Meaning, in every quadrant, there should be theta.
tan(theta) = 1 / sqrt(3) is for theta = 30deg. That's in the 1st quadrant.
For the 2nd quadrant, theta = 180 -30 = 150 deg
For the 3rd quadrant, theta = 180 +30 = 210 deg
For the 4th quadrant, theta = 360 -30 = 330 deg
theta = 30, 150, 210, 330 degrees.