**How to measure angles using protractor**

# How to measure the angle

## Protractor

The most widely known and easy to use tool for measuring angles is the protractor. In order to measure a flat angle with it, it is necessary to align the central opening of the protractor with the top of the angle, and the zero division - with one of its sides. The division value that the second side of the angle crosses is the angle. Thus you can measure angles up to 180 degrees. If it is necessary to measure an angle of more than 180 degrees, it is enough to measure the angle formed by its sides and top and complement it to 360 degrees (full angle), and then subtract the measured value from 360 degrees. The resulting value will be the value of the desired angle.

## Rulers. Bradis Tables

To measure a flat angle, it is enough to add an angle with another side so that a right triangle is formed. By measuring the magnitudes of the sides of the resulting triangle, you can get the value of any trigonometric function of the angle, the value of which you need to know.�Knowing the value of sine, cosine, tangent or cotangent of an angle, you can use the Bradis table to find out the angle.

There are certain known angles that can be measured with a school gon ruler. They produce two types of such lines, both types are right-angled triangles made of wood, plastic or metal. The first type of square is an isosceles right triangle, the two corners of which have a size of 45 degrees. The second type is a right-angled triangle, one of the corners of which is 30 degrees, and the second - 60 degrees, respectively. By matching one of the vertices of the square with the top of the corner and the side with the side of the corner, if the other side of the corner coincides with the adjacent side of the square, you can find the corresponding angle. Thus, with the help of ruler-gons, you can find the angles of 30, 45, 60 and 90 degrees.

## Theodolite

The tools listed in the preceding paragraphs are used to measure angles on a plane. In practice - in geodesy, construction, topography - a special instrument is used to measure the so-called horizontal and vertical angles called theodolite.The main measuring elements of a theodolite are special cylindrical rings (limbs), to which the degree marking is evenly applied. Installed with the help of a special stand at the top of the corner, the device is guided with the help of the telescope, first to the point located on one side of the corner where the measurement is made, then on the other side of the corner, and again to measure. The difference in measurements determines the angle in the first half receiver. Then, the second half is performed in the opposite direction. The arithmetic average of the values obtained in the two semi-receivers is the value of the measured angle.

**Video: How to measure angles using a protractor - why does it have two sets of measurements?**

Student problem#5 :- How to find an angle using measuring Tape.

Measuring angles - Degrees and Protractors

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