For 10 points, name this quadrilateral that has two parallel and two non-parallel sides.
Dagan, Golumbic, and Pinter provided an optimal coloring algorithm for graphs named for this shape. A class of numbers whose members are the sum of at least two consecutive positive integers greater than one is named for this shape. It's not a triangle, but the isosceles type of this shape is cyclic. Along with the rectangle, this shape names a method for approximating integrals. The area of this polygon is equal to half the product of its altitude and the sum of its bases. For 10 points, name this quadrilateral that has two parallel and two non-parallel sides.
Dagan, Golumbic, and Pinter provided an optimal coloring algorithm for graphs named for this shape.
{trapezoid}s [or {trapezium}s; prompt on "quadrilateral" or "polygon"]