Answer:
0 (or 360) and 180 degrees, or 0 and pi. Also, if you are counting all angles included, then the answer is 0, 180, and 360.
Explanation:
tan^2x=0
(tan x)(tan x)=0
If either tangent is 0, the whole expression will also be 0, so you can simplify this expression to simply:
tan x=0
Now, tangent is sin/cos, or on a unit circle the y coordinate value divided by the x coordinate value. If the x coordinate value is 0, then the expression will be undefined. Therefore, this expression is only true when y is 0 and x is not. y is 0 at 0 (or 360) degrees and 180 degrees, making those the only two spots where tanx=0. Hope this helps!