The consecutive angles of a particular trapezoid form an arithmetic sequence. If the largest angle measures $128^\circ$, what is the measure of the smallest angle?
Interior angles sum to 360°
128 + ( 128 - d ) + (128 - 2d ) +(128 - 3d ) = 360
512 - 6d = 360
512 - 360 = 6d
152 = 6d
152 / 6 = d = 76/3
Smallest angle = 128 - 3 ( 76/3) = 128 -76 = 52°
