Isosceles Trapezoids

An isosceles trapezoid has equal legs. It is symmetric: folded along the line through the middles of its bases, one half lands on the other. So its two angles at each base are equal, and figures state that with matching arcs.

Here the bottom angles are 75° each. Along each leg the angles are co-interior, so each top angle is 180 − 75 = 105°. The board reads the equal base angles from the arcs, not from the ticks on the legs: use Marked equal to carry an angle across a base, and Co-interior angles to go up a leg.