One of the rules for polygons is the sum of the exterior angles has to always be equal to 360 degrees. Here we are dealing with a octagon of the regular kind which tells us that each angle on the inside are equal to each other. Here we will use the formula of ((s-2)*180)/s where s is the amount of sides of the shape, we will be using s=8 since it's an octagon. ((8-2)*180).8 = (6*180)/8 = 180/8 = 135 This tells us that every interior angle is equal to 135 degrees The exterior angles are supplementary to the interior angles we will use the formula of 180 - a = b Where A is one angle and B with the supplementary angle 180 - 135 = 45 Thus the exterior angle is at 45 degrees, we could have also done this another way by just doing (360) / 8 which would also give us 45 degrees because another rule of polygons is that the sum of all exterior angles equal 360 degrees and there is 8 angles and since it's a regular octagon thus the 8 angles have to equal eatch other so 360/8 would give us just one of the exterior angles.