A triangle is written of 3 line segments. The heat segments crossing in your endpoints. To surname a triangle we often use the vertices (the surname of the endpoints). The triangle below is named ABC.

You are watching: An isosceles triangle has three congruent sides

A triangle has three angles. The sum of the measures of the angle is always 180° in a triangle.

We have actually different species of triangles. A triangle is classified by the angles and by the variety of congruent sides.

A triangle that has actually three acute angels is dubbed an acute triangle.

A triangle that has one right angle is dubbed a appropriate triangle.

A triangle that has actually one obtuse angle is referred to as an obtuse triangle.

When a triangle has actually three congruent sides, we speak to the triangle an it is intended triangle. We note the congruent political parties by a slash mark. The angle in an it is intended triangle are constantly 60°.

When a triangle has actually two congruent sides it is dubbed an isosceles triangle. The angle opposite to the two sides the the same length are congruent.

A triangle without any congruent sides or angles is called a scalene triangle.

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When two triangles are congruent it method that they have actually the exact same size and also shape. This method that they have the same angles. The red cut marks show us which sides and also angles that are congruent Congruency is shown by this symbol

$$cong$$

$$eginmatrix Acong X & & ABcong XY\ Bcong Y & & BCcong YZ\ Ccong Z & & ACcong XZ endmatrix$$

Triangles that have congruent angles however not the very same size are referred to as similar. Similar triangles have actually sides that space proportional. Similarity is presented by this symbol

$$sim$$

$$igtriangleup ABCsim igtriangleup XYZ$$

$$A=X,: : B=Y,: : C=Z$$

$$fracax=fracby=fraccz$$

**Example**

Find x in the comparable triangles.

We understand that due to the fact that the triangle are comparable the sides room proportional which means that

$$fracx14=frac321Rightarrow$$

$$x=frac14cdot 321=frac4221=2$$

$$x=2$$

**Video lesson**

Find out whether the triangles room right, isosceles, acute, scalene, obtuse or equilateral