tan (theta) + 1 = 0 -----> this means that tan (theta) = -1, right? so theta is the angle where y/x = -1. This means that theta is a 45° angle in the 2nd quadrant or in the 4th quadrant. Expressed in terms of degrees, we would say that theta = 135° or theta = 315°; we can give the answer as a set of values and write { 135°, 315°} for the answer. Or we could express our answer in terms of radians, and in this case, the same angles are = (3pi)/4 radians or (7pi)/4 radians. Sorry that I cannot find the way to type the symbol for "pi" but am hoping you understand! Many times when we give angle measure in radians, we just say the value (like pi/4, or 2pi, etc.) without saying radians after--but we're speaking of measuring angles in radians when you see this kind of answer.