### Geometry of 2D shapes

Term Definition
Area The number of square units needed to cover a given surface
Trapezoid A quadrilateral with exactly one pair of parallel sides
Perimeter The distance around a polygon
Circumference The distance around a circle
Surface Area The sum of the areas of the faces or surfaces of a three-dimensional figure
Prism A polyhedron that has two congruent polygon shaped bases and other faces that are parallelograms
Volume The number of cubic units needed to fill a given space
Parallelogram A quadrilateral with two pairs of parallel sides
Diameter A line segment that passes through the center of a circle and has end-points on the circle or the length of that segment
Radius A line segment with one end-point at the center of a circle and the other end-point on the circle or that length of the segment
area of a rectangle length x width
area of a parallelogram base x height
area of a trapezium ((a +b) x h)/2
Area of a triangle A = (b x h) divided by 2
Circumference of circle Pi x d
Perimeter of a rectangle (and parallelograms) A = 2(L x W)
Triangle Area = 1/2 x base x perpendicular height
Square Area = base x base
Rectangle Area = base x height
Parallelogram Area = base x perpendicular height
Trapezium Area = 1/2 x height x (top + bottom)
Circle Area = ? x r squared
Area (rhombus) bxh
Acute Triangle A triangle with 3 acute angles
Right Triangle A triangle that has a 90 degree angle (right angle)
Obtuse Triangle A triangle with one angle that is greater than 90 degrees.
Square Four equal sides and four right angles
Rhombus A parallelogram with four equal sides
Trapezoid(US)/Trapezium(UK) A quadrilateral with exactly one pair of parallel sides
Pentagon 5 sided polygon
Octagon 8-sided polygon
Nonagon 9 sided polygon
Decagon 10 sided polygon
Heptagon 7 sided polygon
Hexagon 6 sided polygon