2d Shapes

Plane Geometry is the study of flat shapes that you see in pictures or on paper. These shapes include lines, circles, triangles, squares, and rectangles. We call them flat because they have length and width, but no thickness.

A side is a straight edge of a shape.

A vertex (more than one: vertices) is a point where two sides meet.

A polygon is a flat, closed shape made of straight sides that do not cross each other.

Look at the shapes below. Decide if each one is a polygon.\(\quad\)\(\quad\)\(\quad\)

A polygon is named by the number of sides it has. Here are some common polygons:

Triangle	Quadrilateral	Pentagon	Hexagon
3 sides	4 sides	5 sides	6 sides

A regular polygon has all sides the same length and all angles the same size.\(\quad\)\(\quad\)

A rectangle is a quadrilateral (a 4-sided polygon) with four right angles. In a rectangle, opposite sides are equal in length.

To reproduce this shape on graph paper:

1. Place the vertices: Choose one vertex of the original shape as a starting point. Draw this vertex on the grid in the same place. Then count the grid squares to the right/left and up/down to place the other vertices, keeping the same moves as on the original shape.
2. Draw the sides: Use a ruler to join the vertices with straight line segments in the same order as on the original shape.