Answer: the angle is 1°+n×120°
1°, 121°, 241°
Explanation:
Angles are taken modulo 360°, so 363° = 3°.
Angle plus supplement gives 180°.
Let a be angle, s be supplement of a.
So s = 180-a. Given a = 3 + 2s
a = 3 + 2(180 - a)
a = 3 + 360 - 2a = 363 - 2a
3a = 363° or 3° or 723°
a = 121° or 1° or 241°
a = 1°
s = 179°
2s = 358°
2s+3 = 361° = 1° (modulo 360)
a = 121°
s = 180-121 = 59°
2s = 118°
2s + 3 = 121°, as required.
a = 241°
s = 360+180-241 = 540-241 = 299
2s = 598
2s + 3 = 601 = 241 (modulo 360)