# Class 7 Mathematics Chapter 6 | The Triangle And Its Properties TextBook Solutions And Practice Sums

**Summary:**

* The six elements of a triangle are its three angles and the three sides.

* The line segment joining a vertex of a triangle to the midpoint of its opposite side is called a **median** of the triangle. A triangle has 3 medians.

* The perpendicular line segment from a vertex of a triangle to its opposite side is called an **altitude** of the triangle. A triangle has 3 altitudes.

* **An exterior angle** of a triangle is formed, when a side of a triangle is produced.

*** Exterior Angle Sum Property:**

The measure of any exterior angle of a triangle is equal to the sum of the measures of its interior opposite angles.

**The Angle Sum Property of a triangle:**

The total measure of the three angles of a triangle is 180.

* A triangle is said to be **equilateral,** if each one of its sides has the same length.

In an equilateral triangle, each angle has measure 60.

* A triangle is said to be** isosceles**, if at least any two of its sides are of same length.

* The sum of the lengths of any two sides of a triangle is greater than the length of the third side.

*The difference between the lengths of any two sides is smaller than the length of the third side.

* In a right angled triangle, the side opposite to the right angle is called the hypotenuse and the other two sides are called its legs.

***Pythagoras property:**

In a right-angled triangle,

The square on the hypotenuse = the sum of the squares on its legs.