A protractor is a tool for measuring angles.

Knowledge expansion:

A protractor is a tool for measuring angles, which usually consists of a semicircular ruler and a central straight line. Angle can be measured by protractor, which is a common tool in mathematics and geometry.

The invention of protractor can be traced back to ancient times, when people began to use similar tools to measure angles. Modern protractor is generally made of plastic or metal, which has the characteristics of high precision and convenience.

The steps of measuring the angle with a protractor are as follows:

1, the center point of the protractor coincides with the vertex of the angle, and the center line of the protractor coincides with the first side of the angle.

2. Find the angle to be measured, and then align the zero scale line of the protractor with the first side of the angle.

3. Read the angle value, and the value corresponding to the scale line on the other side of the angle to be measured is the angle value to be measured.

In addition to measuring angles, protractors can also be used for other mathematical and geometric problems. For example, the problem of symmetry can be solved with a protractor. By aligning the connecting line between the symmetry axis and the symmetry center and finding the scale line corresponding to the symmetry axis, the scale line corresponding to the symmetry center can be found.

In addition, protractor can also be used to solve the problem of triangle. For example, a protractor can be used to measure the angles of any two internal angles in a triangle, and then the sum theorem of internal angles of a triangle can be used to solve the sizes of other angles.

When using protractor, please pay attention to the following points:

1, the larger the diameter of the protractor, the higher the measurement accuracy, so it is better to choose a larger protractor.

2. When using the protractor, make sure that the center point of the protractor coincides with the vertex of the angle, and the center line of the protractor coincides with the first side of the angle. If it can't be aligned, you need to adjust the position or angle orientation of the protractor.

3. When reading the angle value, you must ensure that the line of sight is perpendicular to the scale line to avoid mistakes.

In a word, protractor is a very practical tool, which is widely used in mathematics and geometry. Mastering the use method skillfully can better solve various angle measurement problems.