NUMBAT OER - Open Educational Resources

2. Two-dimensional shapes

2.1 Quadrilaterals (shapes with four straight sides) and triangles (shapes with three straight sides)

Shape Perimeter Area
(all sides equal and opposite sides parallel, all angles right angles)
4 x x2

(opposite sides equal and parallel, all angles right angles)

2 (x + y) xy

(opposite sides equal and parallel, corner angles not right angles)

(see also note below)

2 (x + y) xh

(two opposite sides parallel but unequal)

x + y + a + b h (y + 0.5 (x -y))
(three sides: special cases where all sides equal = equilateral; and two sides equal = isosceles)
x + y + z 0.5 hz

Note: a parallelogram where all four sides are equal is called a rhombus