The ornamental design for a trapezoidalflatwareset, as shown and described.
FIG. 1 is a top perspective view of the design with broken lines showing fork, spoon and knife heads for the purpose of illustrating environmental structure which forms no part of the claimed design;
FIG. 2 is a top view thereof;
FIG. 3 is a bottom view thereof;
FIG. 4 is a right side view thereof;
FIG. 5 is a left side view thereof;
FIG. 6 is a rear view thereof, looking at the design from a side opposite the shown environmental structure; and,