They both have at least one pair of parallel sides and at least one pair of sides of equal length.
The formulae are quite similar; you multiply base x height, where the height is perpendicular to the base. In the case of a trapezium, you need to calculate the average of the two bases first.
I don't know about the relation in the perimeters of a triangle and a parallelogram but if a triangle is on the same base on which the parallelogram is and the triangle is between the same parallel lines of the parallelogram, then the area of the triangle will be half the area of the parallelogram. That is, area of a triangle = 1/2 area of a parallelogram if the triangle is on the same base and between the same parallel lines.
An Isosceles trapezoid has four sides (is a quadrilateral) with a pair of parallel sides and the other two sides of equal length; whereas An isosceles triangle has three sides with a pair of sides of the same length and the other side a different length.
similarities and differences between ordinary fractions and rational expressions.
A square is a special kind of parallelogram. All four of its sides are the same length and all four of its angles are equal.