Perpendicular lines Two lines are perpendicular if they cross at right angles. You can test this by extending the lines until they cross (if they do not cross then they are parallel). Where the [...]
The perimeter of this rectangle is in dark green. The perimeter of a square or a triangle is the distance all the way around the edge - the green strip in this picture. The circumference of [...]
Two parallel lines Two lines are parallel if they are in the same plane but they can go on forever without ever crossing. You can test this by seeing if you can [...]
A number line is infinite in both directions - definition of a line A line of points A line is made of an infinite number of points that are right next [...]
Geometry: This is an equilateral trangle. What is geometry? The simplest geometric idea is the point, and then the line, the plane, and the solid. Shapes like circles, squares, rectangles, and triangles are flat, and we can think of [...]
This is an isosceles triangle. Definition of an isosceles triangle Isosceles triangles have at least two sides that are exactly the same length. This forces two of their angles to also be acute angles of exactly [...]
This is a hexagon. See, it has six sides that are all the same length. Definition of a hexagon A hexagon is a flat shape, all in one plane, with six [...]
This is an equilateral triangle. What makes a triangle equilateral? Equilateral triangles have all three sides exactly the same length. Because their sides are the same length, the three angles of an equilateral triangle are also [...]
Did you ever have to wrap a basketball as a present? To see how the surface area of a sphere is really 4πr2, find a ball to wrap (a basketball works well). Cut some [...]
A painting with bilateral symmetry - made using mirroring in a paint program To see what bilateral symmetry is, paint a picture. Take a sheet of paper and fold it [...]
