That is 45+k× 180. When k is an even number, all angles are the same as the 45 terminal edge. Similarly, 90+k× 180. When k is an even number, all angles are the same as 90. Terminal edge. That is, 45+k×180 < a/2 < 90+k×180. When k is an even number, it is the first quadrant with a terminal edge of 45 < a/2 < 90.

When k is odd, k = 2n+ 1, 45+k×180 = 45+(2n+1)×180 = 45+180+2n× 65438.

90+k×180 = 90+(2n+1)×180 = 270+2n×180, that is, 45+k× 180.