How to calculate the angle of a roof. We find the side of a triangle if the other two are known in three ways, formulas Calculate degrees knowing the length and height
In mathematics, when considering a triangle, a lot of attention is paid to its sides. Because these elements form this geometric figure. The sides of a triangle are used to solve many geometry problems.
Definition of the concept
Segments connecting three points that do not lie on the same line are called sides of a triangle. The elements under consideration limit part of the plane, which is called the interior of this geometric figure.
Mathematicians in their calculations allow generalizations regarding the sides of geometric figures. Thus, in a degenerate triangle, three of its segments lie on one straight line.
Characteristics of the concept
Calculating the sides of a triangle involves determining all other parameters of the figure. Knowing the length of each of these segments, you can easily calculate the perimeter, area and even the angles of the triangle.
Rice. 1. Arbitrary triangle.
By summing the sides of a given figure, you can determine the perimeter.
P=a+b+c, where a, b, c are the sides of the triangle
And to find the area of a triangle, then you should use Heron's formula.
$$S=\sqrt(p(p-a)(p-b)(p-c))$$
Where p is the semi-perimeter.
The angles of a given geometric figure are calculated using the cosine theorem.
$$cos α=((b^2+c^2-a^2)\over(2bc))$$
Meaning
Some properties of this geometric figure are expressed through the ratio of the sides of a triangle:
- Opposite the smallest side of a triangle is its smallest angle.
- The external angle of the geometric figure in question is obtained by extending one of the sides.
- Opposite equal angles of a triangle are equal sides.
- In any triangle, one of the sides is always greater than the difference of the other two segments. And the sum of any two sides of this figure is greater than the third.
One of the signs that two triangles are equal is the ratio of the sum of all sides of the geometric figure. If these values are the same, then the triangles will be equal.
Some properties of a triangle depend on its type. Therefore, you should first take into account the size of the sides or angles of this figure.
Forming triangles
If the two sides of the geometric figure in question are the same, then this triangle is called isosceles.
Rice. 2. Isosceles triangle.
When all the segments in a triangle are equal, you get an equilateral triangle.
Rice. 3. Equilateral triangle.
It is more convenient to carry out any calculation in cases where an arbitrary triangle can be classified as a specific type. Because then finding the required parameter of this geometric figure will be significantly simplified.
Although a correctly chosen trigonometric equation allows you to solve many problems in which an arbitrary triangle is considered.
What have we learned?
Three segments that are connected by points and do not belong to the same straight line form a triangle. These sides form a geometric plane, which is used to determine the area. Using these segments, you can find many important characteristics of a figure, such as perimeter and angles. The aspect ratio of a triangle helps to find its type. Some properties of a given geometric figure can only be used if the dimensions of each of its sides are known.
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The first are the segments that are adjacent to the right angle, and the hypotenuse is the longest part of the figure and is located opposite the angle of 90 degrees. Pythagorean triangle is called the one whose sides are equal natural numbers; their lengths in this case are called “Pythagorean triple”.
Egyptian triangle
In order for the current generation to recognize geometry in the form in which it is taught in school now, it has developed over several centuries. The fundamental point is considered to be the Pythagorean theorem. The sides of a rectangular is known throughout the world) are 3, 4, 5.
Few people are not familiar with the phrase “Pythagorean pants are equal in all directions.” However, in reality the theorem sounds like this: c 2 (square of the hypotenuse) = a 2 + b 2 (sum of squares of the legs).
Among mathematicians, a triangle with sides 3, 4, 5 (cm, m, etc.) is called “Egyptian”. The interesting thing is that which is inscribed in the figure is equal to one. The name arose around the 5th century BC, when Greek philosophers traveled to Egypt.
When building the pyramids, architects and surveyors used the ratio 3:4:5. Such structures turned out to be proportional, pleasant to look at and spacious, and also rarely collapsed.
In order to build a right angle, the builders used a rope with 12 knots tied on it. In this case, the probability of constructing exactly right triangle increased to 95%.
Signs of equality of figures
- An acute angle in a right triangle and a long side, which are equal to the same elements in the second triangle, are an indisputable sign of equality of figures. Taking into account the sum of the angles, it is easy to prove that the second acute angles are also equal. Thus, the triangles are identical according to the second criterion.
- When superimposing two figures on top of each other, we rotate them so that, when combined, they become one isosceles triangle. According to its property, the sides, or rather the hypotenuses, are equal, as well as the angles at the base, which means that these figures are the same.
Based on the first sign, it is very easy to prove that the triangles are indeed equal, the main thing is that the two smaller sides (i.e., the legs) are equal to each other.
The triangles will be identical according to the second criterion, the essence of which is the equality of the leg and the acute angle.
Properties of a triangle with a right angle
The height that is lowered from the right angle splits the figure into two equal parts.
The sides of a right triangle and its median can be easily recognized by the rule: the median that falls on the hypotenuse is equal to half of it. can be found both by Heron's formula and by the statement that it is equal to half the product of the legs.
In a right triangle, the properties of angles of 30°, 45° and 60° apply.
- With an angle of 30°, it should be remembered that the opposite leg will be equal to 1/2 of the largest side.
- If the angle is 45°, then the second acute angle is also 45°. This suggests that the triangle is isosceles and its legs are the same.
- The property of an angle of 60° is that the third angle has a degree measure of 30°.
The area can be easily found out using one of three formulas:
- through the height and the side on which it descends;
- according to Heron's formula;
- on the sides and the angle between them.
The sides of a right triangle, or rather the legs, converge with two altitudes. In order to find the third, it is necessary to consider the resulting triangle, and then, using the Pythagorean theorem, calculate the required length. In addition to this formula, there is also a relationship between twice the area and the length of the hypotenuse. The most common expression among students is the first one, as it requires fewer calculations.
Theorems applying to right triangle
Right triangle geometry involves the use of theorems such as:
Online calculator.
Solving triangles.
Solving a triangle is finding all its six elements (i.e., three sides and three angles) from any three given elements that define the triangle.
This mathematical program finds the side \(c\), angles \(\alpha \) and \(\beta \) from user-specified sides \(a, b\) and the angle between them \(\gamma \)
The program not only gives the answer to the problem, but also displays the process of finding a solution.
This online calculator may be useful for high school students secondary schools in preparation for tests and exams, when testing knowledge before the Unified State Exam, for parents to control the solution of many problems in mathematics and algebra. Or maybe it’s too expensive for you to hire a tutor or buy new textbooks? Or do you just want to get it done as quickly as possible? homework in mathematics or algebra? In this case, you can also use our programs with detailed solutions.
In this way, you can conduct your own training and/or training of your younger brothers or sisters, while the level of education in the field of solving problems increases.
If you are not familiar with the rules for entering numbers, we recommend that you familiarize yourself with them.
Rules for entering numbers
Numbers can be specified not only as whole numbers, but also as fractions.
The integer and fractional parts in decimal fractions can be separated by either a period or a comma.
For example, you can enter decimals so 2.5 or so 2.5
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A little theory.
Theorem of sines
Theorem
The sides of a triangle are proportional to the sines of the opposite angles:
$$ \frac(a)(\sin A) = \frac(b)(\sin B) = \frac(c)(\sin C) $$
Cosine theorem
Theorem
Let AB = c, BC = a, CA = b in triangle ABC. Then
Square side of triangle equal to the sum squares of the other two sides minus twice the product of these sides multiplied by the cosine of the angle between them.
$$ a^2 = b^2+c^2-2ba \cos A $$
Solving triangles
Solving a triangle means finding all its six elements (i.e., three sides and three angles) from any three given elements that define the triangle.
Let's look at three problems involving solving a triangle. In this case, we will use the following notation for the sides of triangle ABC: AB = c, BC = a, CA = b.
Solving a triangle using two sides and the angle between them
Given: \(a, b, \angle C\). Find \(c, \angle A, \angle B\)
Solution
1. Using the cosine theorem we find \(c\):
$$ \cos A = \frac( b^2+c^2-a^2 )(2bc) $$
3. \(\angle B = 180^\circ -\angle A -\angle C\)
Solving a triangle by side and adjacent angles
Given: \(a, \angle B, \angle C\). Find \(\angle A, b, c\)
Solution
1. \(\angle A = 180^\circ -\angle B -\angle C\)
$$ b = a \frac(\sin B)(\sin A), \quad c = a \frac(\sin C)(\sin A) $$
Solving a triangle using three sides
Given: \(a, b, c\). Find \(\angle A, \angle B, \angle C\)
Solution
1. Using the cosine theorem we obtain:
$$ \cos A = \frac(b^2+c^2-a^2)(2bc) $$
2. Similarly, we find angle B.
3. \(\angle C = 180^\circ -\angle A -\angle B\)
Solving a triangle using two sides and an angle opposite a known side
Given: \(a, b, \angle A\). Find \(c, \angle B, \angle C\)
Solution
1. Using the theorem of sines, we find \(\sin B\) we get:
$$ \frac(a)(\sin A) = \frac(b)(\sin B) \Rightarrow \sin B = \frac(b)(a) \cdot \sin A $$
Let's introduce the notation: \(D = \frac(b)(a) \cdot \sin A \). Depending on the number D, the following cases are possible:
If D > 1, such a triangle does not exist, because \(\sin B\) cannot be greater than 1
If D = 1, there is a unique \(\angle B: \quad \sin B = 1 \Rightarrow \angle B = 90^\circ \)
If D If D 2. \(\angle C = 180^\circ -\angle A -\angle B\)
3. Using the sine theorem, we calculate the side c:
$$ c = a \frac(\sin C)(\sin A) $$
In geometry, an angle is a figure that is formed by two rays that emerge from one point (called the vertex of the angle). In most cases, the unit of measurement for angle is degree (°) - remember that a full angle, or one revolution, is 360°. You can find the angle value of a polygon by its type and the values of other angles, and if given a right triangle, the angle can be calculated from two sides. Moreover, the angle can be measured using a protractor or calculated using a graphing calculator.
Steps
How to find interior angles of a polygon
- For example, a triangle has 3 sides and 3 interior angles, and a square has 4 sides and 4 interior angles.
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Calculate the sum of all interior angles of the polygon. To do this, use the following formula: (n - 2) x 180. In this formula, n is the number of sides of the polygon. The following are the sums of the angles of commonly encountered polygons:
- The sum of the angles of a triangle (a polygon with 3 sides) is 180°.
- The sum of the angles of a quadrilateral (a polygon with 4 sides) is 360°.
- The sum of the angles of a pentagon (a polygon with 5 sides) is 540°.
- The sum of the angles of a hexagon (a polygon with 6 sides) is 720°.
- The sum of the angles of an octagon (a polygon with 8 sides) is 1080°.
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Divide the sum of all the angles of a regular polygon by the number of angles. A regular polygon is a polygon with equal sides and equal angles. For example, each angle of an equilateral triangle is calculated as follows: 180 ÷ 3 = 60°, and each angle of a square is calculated as follows: 360 ÷ 4 = 90°.
- An equilateral triangle and a square are regular polygons. And at the Pentagon building (Washington, USA) and road sign"Stop" shape of a regular octagon.
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Subtract the sum of all known angles from the total sum of the angles of the irregular polygon. If the sides of a polygon are not equal to each other, and its angles are also not equal to each other, first add up the known angles of the polygon. Now subtract the resulting value from the sum of all the angles of the polygon - this way you will find the unknown angle.
- For example, if given that the 4 angles of a pentagon are 80°, 100°, 120° and 140°, add up these numbers: 80 + 100 + 120 + 140 = 440. Now subtract this value from the sum of all the angles of the pentagon; this sum is equal to 540°: 540 - 440 = 100°. Thus, the unknown angle is 100°.
Advice: the unknown angle of some polygons can be calculated if you know the properties of the figure. For example, in an isosceles triangle, two sides are equal and two angles are equal; In a parallelogram (which is a quadrilateral), opposite sides are equal and opposite angles are equal.
Measure the length of the two sides of the triangle. The longest side of a right triangle is called the hypotenuse. The adjacent side is the side that is near the unknown angle. The opposite side is the side that is opposite the unknown angle. Measure the two sides to calculate the unknown angles of the triangle.
Advice: use a graphing calculator to solve the equations, or find an online table with the values of sines, cosines, and tangents.
Calculate the sine of an angle if you know the opposite side and the hypotenuse. To do this, plug the values into the equation: sin(x) = opposite side ÷ hypotenuse. For example, the opposite side is 5 cm and the hypotenuse is 10 cm. Divide 5/10 = 0.5. Thus, sin(x) = 0.5, that is, x = sin -1 (0.5).
Count the number of sides of the polygon. To calculate the interior angles of a polygon, you first need to determine how many sides the polygon has. Note that the number of sides of a polygon is equal to the number of its angles.
ANDREY PROKIP: “MY LOVER IS RUSSIAN ECOLOGY. YOU NEED TO INVEST IN IT!”
On September 4-5, the environmental forum “Climatic Shape of Cities” was held. The initiator of the event is the C40 organization, which was founded in 2005 by the UN. The main task of the form and cities is to control climate change cities.
As practice has shown, in contrast to social events and “meetings in nightclubs,” there were few deputies and public figures. Among those who did identify concerns environmental situation was Prokip Adrey Zinovievich. He took an active part in all plenary sessions together with the Special Representative of the President Russian Federation on climate issues Ruslan Edelgeriev, Deputy Mayor of Moscow for Housing and Communal Services Pyotr Biryukov, as well as foreign representatives - the mayor of the Italian city of Savona - Ilario Caprioglio. Participants presented their projects and also discussed strategies to curb the rise in global temperatures, as well as proposed practical solutions sustainable development cities.
ANDREY PROKIP ABOUT SHASHLIKS, DEPUTIES AND GREEN BUILDING
Of particular interest to Russian side caused a presentation by speakers, among whom were European architects, scientists and the Mayor of Savona. The topic of the speech was the TOP direction - “green construction”. As Andrey Prokip himself stated, “it is important to correctly redistribute resources, as well as take into account European construction standards for a metropolis like Moscow. It is necessary for Russia to take a course towards “green financing” at the Federal level, especially since it is economically feasible and, as practice shows, profitable.” He also expressed concerns about the deterioration of the health of Russians due to environmental disasters and non-compliance with environmental standards for waste disposal by large and small industrial enterprises" He was also confirmed in his fears thanks to the speech of Francesco Zambona, a professor at the WHO European Office for Investment in Health.
With characteristic humor, Andrei addressed famous people who were invited to the forum, but never showed up, with a call to “remember nature, not only when they want barbecue or go fishing. After all, the health of the entire people depends on the benevolence of nature, which, unfortunately, includes them.”
In addition to passionate speeches about Andrei Zinovievich’s new “lover-nature” and the importance of taking responsibility for environment itself, a significant event of the forum was plenary session on the topic “How to raise a new generation.” The forum participants were unanimous in the opinion that it is necessary to educate not only children, but also the adult generation. It is very important to instill responsibility towards nature in everyday behavior, as well as in business.
A special project “learning to live in a civilized manner” will be launched for Moscow. This educational project for all segments of the population and age categories. But no matter how wonderful the theory and good intentions are, the saying “until the roast rooster pecks, the fool will not cross himself” is still relevant for Russia.
According to Timothy Netter, a famous theater director, art can change everything. In one of his speeches, he talked about how the idea of preserving nature should be presented in theater and cinema and how important it is to educate people through art to be responsible for what will happen to us and nature tomorrow.
Students from Russian universities attracted the attention of Rentv operators and Andrey Prokirpa by presenting a project on environmentally friendly technology for the production of containers that are resistant to moisture and temperature. This is a very pressing problem, since laws are being passed around the world against plastic containers, which, by the way, take more than 30 years to decompose, pollute the soil and cause the death of animals.
It is encouraging that Moscow is one of 94 participating cities in the C40 organization and this is the third time the forum has been held, which every year attracts the attention of more and more famous personalities and citizens.
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