Geo-Math-Knecht

Front 1

radius

Back 1

The circle is a set of points equally distant from one central point. This central point is called the center of the circle. Here the center is shown with a small cross. The distance from the center to the curve of the circle is called the radius. Here the radius is shown as a line from the center to the curve of the circle.

Front 2

diameter

Back 2

The distance across the circle is called the diameter. The diameter always passes through the center of the circle. The diameter is equal in length to twice the radius.

Front 3

circumference

Back 3

The distance all the way around the circle is called the circumference. The circumference is usually symbolized with a 'C' as shown here. The length of the circumference is equal to 2 times pi times the radius.

Usually, as here, the radius is symbolized with an 'r'

Front 4

rhombus

Back 4

The rhombus is a quadrilateral with all sides equal in length. Notice that it is a parallelogram, since opposite sides are parallel.

Front 5

The area of the rhombus

Back 5

Since the rhombus is a parallelogram, you find its area using the same method that you would use for a parallelogram.

The length of the base of the rhombus is the length of one of its sides, here shown with 'b'.

The height is the perpendicular distance between opposite sides, here shown with an 'h'.

The area of the rhombus is equal to its base times its height, or:

area = bh

Front 6

The diagonals of a rhombus

Back 6

The diagonals of a rhombus are perpendicular.

Front 7

is a square a rhombus

Back 7

A square is a rhombus since it is a quadrilateral with all sides equal.

Front 8

trapezoid

Back 8

The trapezoid is a quadrilateral with one pair of parallel sides.