**Annotation**

Plane angles need to be divided into trigonometrical angles and rotation angles.

**Measurement of angles in a solid geometry**

In a solid geometry «angle between a straight line and the plane is called angle between this line and its projection (orthogonal) to the plane. If the straight line to be a perpendicular plane, then angle between it and the plane is

*considered*(my italic type – Nikolaj Khizhnjak) equal 90°, and between a parallel straight line and the plane – equal 0°". [1, p. 308].

As appears from definition, the angle between a straight line and the plane cannot be more than 90°. Angles more than 90° fall into to angles of rotation [2, p. 81]. In a solid geometry it is not accepted to describe by means of angles rotation of a straight line around a point of its crossing with the plane.

If the straight line is parallel to the plane (or belongs to the plane), then it is

*considered*, that the size of the angle has zero value. Actually there is no vertex of angle – a cross point of a straight line and the plane. If the perpendicular plane straight line, then a trace turns into a point which coincides with a cross point of a straight line and the plane. Actually there is no second ray forming a angle. In this case the angle is

*considered*right angle.

**Measurement of angles in a planimetrics**

On analogies to a solid geometry,

**a plane angle between two straight lines (line segments) it has to be measured as a angle between a point on one direct and its projection on other straight line with vertex of angle in a cross point of these straight lines**.

This rule allows to divide plane angle into

**trigonometrical angles**(from 0° to 90°) and

**rotation angles**. The fundamental difference between these angles consists in amount of the objects on the two dimensional plane forming a angle. The trigonometrical angle is measured between two different objects, the rotation angle is measured between two provisions (initial and terminating) one object. For trigonometrical angles the time factor is absent, for rotation angles the time factor is obligatory: tentative situation, rotation time, terminating situation.

At measurement of angles between two parallel straight lines the angle cannot be defined because there is no cross point of straight lines. At measurement of a corner between two perpendicular straight lines the angle cannot also be defined because the projection of a point coincides with a cross point of these straight lines.

**Conclusion: zero and right angles cannot have just the same mathematical properties as other angles.**In more detail these distinctions will be described by consideration of trigonometric functions.

**Angles and distances**

The trigonometrical angle on the properties is similar to distance between two points, the rotation angle is similar to the passable way between the same points. If driving is carried out in a straight line, then the passable path is equal to distance between initial and terminating points of a way. If rotation is carried out on a angle to 90°, then the angle of rotation is equal to a trigonometrical angle. The rotation angle cannot be less trigonometrical angle, the passable path cannot be less than a distance between points of the beginning and end of this way. The distance between two points can be in the numerical range from zero ad infinitum. Compliance between angles from 0° to 90° and numbers from zero ad infinitum is established by a trigonometric function of a tangent of these angles.

The passable path is also expressed in the numerical range from zero ad infinitum even if the distance between an initial and finishing point of the passable way is equal to zero. In the same way the rotation angle can reach infinitely great values, at the same time the trigonometrical angle between the beginning and the end of rotation can be equal to zero. In this case it is possible to establish direct analogy between number and size of a angle as it is accepted in a calculus.

Various mathematical tools, for example, a Pythagorean theorem are used to calculation of distance between initial and terminating points of the passable path. Reduction formulas of angles are applied to definition of a angle between the beginning and the end of rotation.

**Conclusion:**plane angle on the properties are similar to distances on the plane.

**Literature**

1. Zabelyshynskaia M.Y."Mathematician. Educational and practical reference book" Kharkiv, Ranock, 2010.

2. Khizhnjak Nikolaj «Bases of mathematics», The Papers of Independent Authors, vol. 19, 2011.

P.S. This article is published for a warming up. Article about trigonometric functions in a rectangle will be a headliner of new work. I hope, from it you learn a lot of new and interesting.

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