Notes
two congruent quadrilaterals and a rectangle solution

Two Congruent Quadrilaterals and a Rectangle

Two Congruent Quadrilaterals and a Rectangle

Two congruent quadrilaterals and a rectangle. Which shaded region is larger, yellow or green?

Solution by Triangle Area and Congruent Shapes

Two congruent quadrilaterals and a rectangle labelled

As the line segment GCG C is common to both shapes, they are related by a rotation of 180 180^\circ about a point which can be found by joining two corresponding points, such as AA and EE, and finding its midpoint, which is II. In particular, AIA I and IEI E are of equal length.

Since BHB H is parallel to ACA C, the perpendicular distances of BB and HH abvoe ACA C are equal, so triangles ABCA B C and AHCA H C have the same area. Then as AIA I and IEI E have the same length, triangles AIHA I H and IEHI E H have the same area. Putting these together shows that regions ABCIA B C I and IEHI E H have the same area. Therefore the yellow and green regions have equal area.