Let F1 be the set of all parallelograms, F2 the set of rectangles, F3 the set of rhombuses, F4 the set of squares and F5 the set of trapeziums in a plane, then F1 is equal to
F2∪F3∪F4∪F1
Every rectangle, rhombus and square in a plane is a parallelogram but every trapezium is not a parallelogram.
Hence,
F1=F2∪F3∪F4∪F1