### Understanding Elementary Shapes Summary

### Two Dimensional Figures

The closed figure formed by joining three line segments end-to-end is called a

**triangle**. Each line segment forms a side of the triangle.**Scalene triangle**

A triangle is called a scalene triangle if all the three sides are of unequal length.

**Isoceles triangle**

**Equilateral triangle**

A triangle is said to be an equilateral triangle if the lengths of all of its sides are equal.

**Acute-angled triangle**

If all the angles of a triangle are less than 90°, then the triangle is called an acute-angled triangle.

**Right-angled triangle**

If one of the angles in a triangle is a right angle, then the triangle is called a right-angled triangle.

**Obtuse-angled triangle**

If one of the angles in a triangle is an obtuse angle, then the triangle is called an obtuse-angled triangle.

**Parallelogram**

A parallelogram is a four-sided figure in which the opposite sides are parallel to each other and are of equal length. In a parallelogram, the diagonals need not be equal in length.

**Rectangle**

A rectangle is a type of parallelogram that has opposite sides equal in length and parallel to each other. Its diagonals are equal in length. A rectangle has four right angles.

**Square**

A square is a type of parallelogram in which all the four sides are equal in length. Its diagonals are equal in length. A square has four right angles.

**Rhombus**

In a rhombus, all the sides are equal in length, and the opposite sides are parallel to each other. Its diagonals are not equal in length. Also, the opposite angles are equal to each other.

**Trapezium**

A trapezium has one pair of sides parallel to each other. The other two sides are not parallel to each other.

**Polygon**

A polygon is a closed figure with three or more than three sides.

### Three Dimensional Shapes

**Solid figures**have three dimensions - length, breadth and height. e.g. A ball, a brick, an ice cream cone and a can.

**Face**

The flat surface of a solid shape is called a face.

**Edge**

Two faces of a solid shape meet on a line segment called an edge.

**Vertex**

A vertex of a solid shape is a point where three or more edges meet.

**A cuboid**has 6 faces, 12 edges and 8 vertices.

Prisms and pyramids are named after their bases. The base of a prism can be of any polygonal shape.

There are 5 faces, 9 edges and 6 vertices in a

**triangular prism**.
There are 4 faces, 6 edges and 4 vertices in a triangular

**pyramid.**

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