A dodecagon has 12 sides
The way I remember is "decagon = 10 sides" and "do = duo = 2" so 10+2 = 12.
The measure of each exterior angle of a regular polygon is found by this formula
E = 360/n
plug in n = 12 to get
E = 360/n
E = 360/12
E = 30
Each exterior angle of a regular dodecagon is 30 degrees. The interior angle is 180-E = 180-30 = 150 degrees
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Interior angle = 150 degrees
Exterior angle = 30 degrees
Subtract the values: 150 - 30 = 120
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Final Answer: 120 degrees