The word “Plane” in dictionary says,

- Level
- Flat surface
- For smoothing surface

In math, **plane is defined as the levelled flat smooth surface.**

Plane figures are those figures which are closed and has smooth levelled flat surface.

Plane figures boundary could be straight lines or curved lines or both.

Illustration:

It is a plane figure since it is closed The boundary of the plane figure is a curved line | |

It is a plane figure since it is closed The boundaries of the plane figure has straight and curved lines. | |

It is a plane figure since it is closed The boundary of the plane figure has straight lines. | |

It is a plane figure since it is closed The boundaries of the plane figure has straight and curved lines. | |

It is a plane figure since it is closed The boundary of the plane figure has straight lines. |

It is not a plane figure since it is not closed. | |

It is not a plane figure since it is not closed. |

## Identification of Plane Figures

Identify whether the following alphabets are plane figures.

A A is not a plane figure. (Not closed)

B B is a plane figure. (Closed)

M M is not a plane figure. (Not closed)

D D is a plane figure. (Closed)

Z Z is not a plane figure. (Not closed)

O O is a plane figure. (Closed)

## Properties of Plane Figures:

1.Plane figures that are completely made of straight lines make angles at the

intersection of two lines.

Number of sides = number of angles

**Example:**

A triangle has three angles.

A rectangle has four angles.

A pentagon has five angles

Illustration with a hexagon.

2. Any three non collinear points lie on one and only one plane.

3. Plane is a two dimensional figure.

4. Plane figures area and perimeter can be determined.

5. Plane figures do not have volume.

**Illustration:**

This is a cube whose volume can be determined. But this is not a plane figure.

A three dimensional object has volume whereas plane figures are two dimensional.