Every triangle has three sides. The sides allow us to classify the different types of triangles according to their size.

For example, a triangle with two equal sides (edges) is an isosceles triangle and one in which all its sides (edges) are equal is an equilateral triangle. While a triangle that has all its sides different is an equilateral triangle.

If an equilateral triangle has perimeter $P=21\operatorname{cm}$. How long is each side?

Solution

Since the triangle is equilateral we know that its sides are equal, so we just divide the perimeter by three to get the measure of each side. lado.

$P=3x$

$21\operatorname{cm}=3x$

$x=21\operatorname{cm}:3$

Answer:

$x=7\operatorname{cm}$

Example 4

Tell if it is possible to construct a triangle in which its sides measure $5~cm$, $7~cm$ and $10~cm$.

Solution

We add the lengths of any two sides (edges) and compare with the length of the remaining side.

$5~cm + 7~cm= 12~cm$which is greater than the remaining side that measures $10~cm$

$7~cm + 10~cm = 17~cm$The length of the remaining side, which is greater than the remaining side measuring $5~cm$, is greater than the remaining side measuring $5~cm$.

$10~cm + 5~cm = 15~cm$, which is greater than the remaining side measuring $7~cm$.

Answer:

So if it is possible to construct a triangle of measures $5~cm$, $7~cm$ and $10~cm$ on each side.

Check your understanding

Question 1

Is the straight line in the figure the height of the triangle?

The edges of a triangle, commonly called the sides of a triangle, are the straight lines that bound the faces of the triangle.

What are the edges of a figure?

In a plane figure, the edges or sides are the line segments that join two vertices, and form the outline or perimeter of the figure.

Exercises on the sides or edges of a triangle

Exercise 1

Query

$DE$ Does that side not exist as part of any of the triangles?

Solution

A side in a triangle is a line that passes between one of the 3 points that are the angles of the triangle.

In this case the line $DE$ does not pass between the extreme angles of any of the triangles but goes out through a point $D$ which is in fact an angle in a triangle $\triangle DBC$ but $DE$ ends at the point $E$ which is not an angle in any of the triangles in the figure.

To solve the task we replace all the data we have in the equation to calculate the perimeter of the triangle:

$2X+3X+3.5X=17$

Let's remember... The perimeter of the triangle is equal to the sum of its 3 sides.

If we calculate the equation we find that:

$8.5X=17$

We divide the equation by $8.5$ to find the value of. $X$

$\frac{8.5X}{8.5}=X=\frac{17}{8.5}=2$

Answer

$2$

Exercise 5

Request

Given the equilateral triangle

The perimeter of the triangle is $33\operatorname{cm}$, what is the value of $X$?

Solution

One of the characteristics of an equilateral triangle is obviously that each of its sides are equal, i.e. if one side is worth $11$ all its sides will be equal to $11$

Answer

$11$

Do you know what the answer is?

Question 1

Is the straight line in the figure the height of the triangle?

examples with solutions for the sides or edges of a triangle

Exercise #1

Given the following triangle:

Write down the height of the triangle ABC.

Video Solution

Step-by-Step Solution

An altitude in a triangle is the segment that connects the vertex and the opposite side, in such a way that the segment forms a 90-degree angle with the side.

If we look at the drawing, we can notice that the previous theorem is true for the line AE that crosses BC and forms a 90-degree angle, comes out of vertex A and therefore is the altitude of the triangle.

Answer

AE

Exercise #2

ABC is an isosceles triangle.

AD is the median.

What is the size of angle $∢\text{ADC}$?

Video Solution

Step-by-Step Solution

In an isosceles triangle, the median to the base is also the height to the base.

That is, side AD forms a 90° angle with side BC.

That is, two right triangles are created.

Therefore, angle ADC is equal to 90 degrees.

Answer

90

Exercise #3

Which of the following is the height in triangle ABC?

Video Solution

Step-by-Step Solution

Let's remember the definition of height of a triangle:

A height is a straight line that descends from the vertex of a triangle and forms a 90-degree angle with the opposite side.

The sides that form a 90-degree angle are sides AB and BC. Therefore, the height is AB.

Answer

AB

Exercise #4

True or false?

$\alpha+\beta=180$

Video Solution

Step-by-Step Solution

Given that the angles alpha and beta are on the same straight line and given that they are adjacent angles. Together they are equal to 180 degrees and the statement is true.

Answer

True

Exercise #5

Three angles measure as follows: 60°, 50°, and 70°.

Is it possible that these are angles in a triangle?

Video Solution

Step-by-Step Solution

Recall that the sum of angles in a triangle equals 180 degrees.

Let's add the three angles to see if their sum equals 180:

$60+50+70=180$

Therefore, it is possible that these are the values of angles in some triangle.