What is a Quadrilateral? | Don't Memorise

A vertex is formed where two sides meet, and the space between those sides is called an angle. A quadrilateral has four angles. Angles can be named based on the vertex (e.g., angle A) or more precisely using three vertices (e.g., angle DAB or BAD).

A television screen, an envelope, or a canvas are all examples of quadrilaterals. The word 'quadrilateral' comes from 'quadri' meaning four, and 'lateral' meaning sides. All these examples have four sides.

To name a quadrilateral, we label its four points (corners) as A, B, C, and D. These points are called vertices, and every quadrilateral has four vertices. The sides are formed by connecting these vertices, for example, AB, BC, CD, and DA. A quadrilateral is a closed figure lying on a single plane.

Vertices opposite to each other, like A and C, or B and D, are connected by lines called diagonals. For example, AC and BD are diagonals. Diagonals have practical applications, such as in screen measurements; a 17-inch laptop or a 51-inch TV refers to the length of its diagonal.

In summary, a quadrilateral is a closed figure on one plane that has four sides, four vertices, and four angles.