## How to find the cosine of the angle of a triangle with vertex

Instruction 1 For an arbitrary triangle with vertices A, B and C, the problem of finding the cosine is the same for all three angles if triangle island.\$ If there is a blunt angle in the triangle, the definition of its cosine should be considered separately. 2 In the island-angle triangle with vertices A, B … Read more

## How to prove that a segment is a bissectry

You will need – notebook; – pencil; – ruler. Instruction 1 It is impossible to prove a theorem without knowledge of its constituents and their properties. It is important to pay attention to the fact that the bisector of the angle, according to the generally accepted concept, is a beam that emerges from the vertex … Read more

## What is arshin and pud

The Russian system of measurement was used in Russia, and later — in the Russian Empire until 1918. At the turn of the century (in June 1899), an ordinance was made to use the metric system of measures, but in a non-binding manner. And only the decree of September 14, 1918 and July 21, 1925 … Read more

## How to prove that a triangle isoscele

Instruction 1 In an isosceles triangle, two equal sides are called lateral, and the third is the base of the triangle. The intersection point of equal sides is the vertex of the isosceles triangle. The angle between the same sides is considered the angle at the vertex, and the other two are the angles at … Read more

## How to fit a square into a circumstance

You’ll need -circular -pencil -clutch -scissors Instructions 1 Draw a sketch to the task. Obviously, the diameter of the circle is the diagonal of the square inscribed in this circle. Remember the known property of a square: its diagonals are mutually perpendicular. Use this diagonal relationship when constructing a given square. 2 Draw the diameter … Read more

## Who came up with Arabic numbers

The name “Arabic numerals” is the result of a historical error. They came up with these signs to record the number by no means Arabs. The error was corrected only in the XVIII century by the efforts of G.Y.Ker — the Russian Orientalist scientist. It was he who first suggested that the figures traditionally referred … Read more

## How to find a diamond angle

Instruction 1 The sum of the four inner corners of a diamond is 360°, as in any quadrangle. The opposite angles of the rhombus are equal, while always in one pair of equal angles – the angles are sharp, in the other – blunt. Two corners adjacent to one side in sum make up the … Read more

## How to find symmetry center

Instruction 1 If two points are given, the center of symmetry between them, by definition, will be the middle of the line connecting them. This is more difficult to deal with the geometric figure: here it is already necessary to consider all the points that make up it. Any arbitrary point must pass to a … Read more

## How to make a proper octahedr

You will need – dense paper or cardboard; – ruler; – pencil; – protractor; – scissors; – PVA glue. Instruction 1 The octahedron has eight faces, each of which is an equilateral triangle. In geometry, it is common to construct an octahedron inscribed in or described near a cube. To make a model of this … Read more