MATHINFINITY

PROTRACTOR

Protractor is used for measuring or drawing angles. It is usually made of plastic, wood or metal. It originated when the Arabs divided a straight angle into 180 parts. People later followed it and made the protractor.

The half circular protractor or circular protractor is commonly used in Mathematics. The half circular protractor is a semi-circle marked from 0 to 180 degrees. When there were no electronic measuring tools or computer drawing software, ruler, triangular ruler and compass, in addition to protractor, are the necessary tools for measuring and drawing.

Measuring Angles

Place the protractor over the angle. Align the vertex of the angle with the origin (centre point) of the protractor. Rotate the protractor so that one leg of the angle falls on the baseline (line projecting to the start of the scale) of the protractor. Follow the opposite leg of the angle up to the measurements on the protractor's arc. The number that this leg passes through is the angle's measurement in degrees.

Drawing Angles

Draw a straight line. Place the origin of the protractor at one end of the line. This point will be the vertex of the angle. Align the line with the baseline of the protractor. Find the degree of the angle you wish to draw on the protractor's appropriate scale, and then mark the degree with a dot. Connect the vertex with the marked degree using a ruler. This second line completes your angle.

Interactive Game

We know that the interior angle of a regular hexagon is 120°. There is a chair with the same angle of 120° in the exhibition gallery.

Did you know?

If you cut a circular cake three times into six equal parts, each slice will have an angle of 60o. If you share all the six slices among three children, each will get two slices. These two slices together is equal to 120° of the cake.