Important topic of Chapter 7 – Triangles Class 9 Maths
9 Class Maths : After reading this article, the student will able to understand the concept of the triangle and the types of the triangle on the basis of sides and the angle measurement.
Definition:- Triangle is a plane figure surrounded by three line segments. The symbol of Triangle is ∆.
Example – ∆ PQR – It represents PQR as a triangle with three vertices P, Q, And R. ∆ PQR has three sides PQ, PR, QR and ∠P, ∠Q, ∠R are three angles in a ∆PQR. Every triangle has 3 sides and 3 angles.
Types of angle on the basis of sides
On the basis of Sides – there are three types of triangles
- Equilateral Triangle: – In an equilateral triangle, all sides are equal. In the below figure, PQR is a triangle in which PQ=QR=PR, so it is an equilateral triangle.
- Isosceles Triangle: -A triangle having two sides equal is called an isosceles triangle. In the below figure ABC is a triangle in which AB=AC, hence it is an isosceles triangle.
- Scalene triangle– A triangle in which all the sides are of different in size is called a scalene triangle. In the below figure DEF is a triangle in which no side is equal.
- Perimeter of a triangle– The sum of lengths of three sides of a triangle is called its perimeter.
- Types of Triangles on the basis of angles – On the basis of angles, triangles are divided into 3 categories:-
- Right angled triangle– A triangle in which one of the angles measures 90⁰ is called a right angled triangle or simply a right triangle. In a right-angled triangle, the side opposite to the right angle is called its hypotenuse and the remaining two sides are called its legs.
- Acute angled triangle– A triangle in which every angle measures more than 0⁰ but less than 90⁰ is called an acute-angled triangle. In the below figure if we will observe we will find that every angle is an acute angle.
- Obtuse-angled triangle-A triangle in which one of the angles measures more than 90⁰ but less than 180⁰ is called an obtuse angled triangle.
Types of triangles on the basis of angles
In the next article, will discuss the terms related to the triangle and theorem related to the triangles.
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