This is a straight line.

Straight lines are classified into three types, viz. standing/vertical lines, sleeping/horizontal lines and slanting/oblique lines. In general, these three types are mutually exclusive, i.e., a line **cannot be both** horizontal and vertical. The type of line is based on certain frame of reference. For example: A vertical line is called so because it may be parallel to the side edges of the paper. To classify the lines as horizontal, vertical and oblique there is always a frame of reference to be considered. The stick figures represent standing, sleeping and slanting lines.

A curved line is a line with smooth bends or humps. This is a curved line.

## Open and closed figures

A closed figure can be made of straight or curved lines. It has no opening. Given below is an example of a closed figure.

An open figure is made of either straight or curved lines. However, it has at least one opening. Given below is an example of an open figure.

## Plane shapes

Plane shapes are 2D shapes that have length and breadth but have no depth or thickness. The different types of plane shapes are given below.

This is a square. Square is a four sided closed figure.

This is a rectangle. A rectangle is also a four sided closed figure.

This is a triangle. A triangle is a three sided closed figure.

This is an oval. It has no sides or corners.

This is a circle. It has no sides or corners.

## Sides and corners

We have learnt what plane shapes are and what they look like. Plane shapes are two dimensional, e.g., squares, triangles, and circles. The straight lines that make up a plane shape are called sides. The points where two sides meet are called corners.

## Tips and tricks

- Count the number of sides to identify the shapes
- Use paper cut-outs to visualise the shapes
- Use everyday objects trace the surface and identify the plane shapes

### Common mistakes or misconceptions

**Misconception 1:** Circle and oval are not a closed figures. As they are not made of straight lines.

A closed figure can be made of any line (curved or straight) it should not have any openings. A circle has no opening. And hence it is a closed figure. The picture given below will help understand this better.

**Misconception 2: **The given figure has 5 sides.

The straight lines that make up a plane shape are called sides. The line segment in the middle of the shape is not making up the plane shape and hence is not a side.

## Test your knowledge

- How many corners does a square have? __________
- How many corners does a triangle have?__________
- How many sides does a triangle have? ___________
- How many sides are there in a square? ___________
- How many corners does a circle have? ___________