Help With Shapes, Angles and Polygons: A Parent’s Guide

Helping With Elementary School Geometry

While elementary school geometry may not deal with proofs or theorems, students do learn a lot about angles and shapes. Remembering what all those shapes and angles are can be hard without a visual aid, so here are some of the basic terms illustrated to help you out.

Acute Angle

acute angle
Amanda Morin

An angle is the space or distance between two line segments at the point at which they meet. Angles are measured in degrees. An acute angle is an angle that measures less than 90 degrees.

Obtuse Angle

obtuse angle
Amanda Morin

An obtuse angle is an angle that measures more than 90 degrees. Many children are taught to think of obtuse angles as the ones that are stretching out and relaxing.

Right Angle

right angle
Amanda Morin

A right angle is an angle that measures exactly 90 degrees. It is denoted by a square inside the angle. A right angle can be thought of as an angle that is sitting up as straight as it can.


circle radius
Amanda Morin

Technically, a circle is the shape drawn around a collection of points that measure an equal distance from the center of all those points. The radius of a circle, the line drawn from that center to any of the points, is always the same measurement no matter to which point it’s connected.

Convex and Concave

convex concave
Amanda Morin

A convex shape is one in which you can connect any two points that make up the figure and the line segment is inside the shape. In others words, there’s no negative space.

A concave shape has negative space, so a line segment connecting two points can conceivably be drawn outside the shape.

Equilateral Triangle

equilateral triangle
Amanda Morin

An equilateral triangle is a triangle in which all the sides are the same length. This also means that all the angles will measure the same number of degrees.

Isosceles Triangle

Isosceles Triangle
Amanda Morin

An isosceles triangle has two sides of equal length and one side whose length is not the same as the other two.

Scalene Triangle

Scalene triangle
Amanda Morin

A scalene triangle’s side are all different lengths. Often a scalene triangle will contain an obtuse angle.


Amanda Morin

Polygons are closed shapes made up of line segments. Each line segment connects to the end of two other line segments.  Regular polygons have sides and angles all of the same length and measurements, such as a square or a hexagon.

Rectangles, for example, are not regular polygons because the sides are not all the same length.  Shapes with curved sides, like ovals and circles, are not polygons either.


Amanda Morin

Both intersecting rays or line segments and polygons have a vertex (or vertices). In intersecting line segments, the vertex is the point at which the two intersect, where the angle is.  The vertices of a polygon  are the points at which each side meets another side. A multi-sided polygon can have a number of vertices.

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