 Triangles - Orchids The International School
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Triangles

• A triangle is a two-dimension closed figure.
• It has three sides and three interior angles.
• The point where two sides intersect each other is called the vertices of the triangle.
• A triangle has three vertices. Types of Triangles

1. Based on the length of the sides of a triangle:

A triangle is of three types:

• Equilateral triangle
• Isosceles triangle
• Scalene triangle

Equilateral Triangle

In an equilateral triangle, the length of all the sides of the triangle is equal. Isosceles Triangle

In an isosceles triangle, the length of any two sides of the triangle is equal. Scalene Triangle

In a scalene triangle, the length of all the sides of the triangle is unequal. 2. Based on Angle:

There are three types of triangles:

• Acute angled triangle
• Obtuse angled triangle
• Right-angled triangle

Acute angled Triangle

When each of the angles of a triangle is less than 90° is called an acute-angled triangle or acute triangle.

Obtuse angled Triangle

When any one of the angles of a triangle is more than 90° is called an obtuse-angled triangle or obtuse triangle.

Right angled Triangle

When any one of the angles of a triangle is equal to 90° is called a right-angled triangle or right-angled triangle or right triangle.

3. Based on Angle and Sides: Angles in Triangle

• There are three angles in a triangle.
• The sum of the angles of a triangle is equal to 180°. The sum of the angle = 45° + 90° + 45° = 180°
Therefore, the given figure is a triangle. The sum of the angle = 75° + 56° + 88° = 219°
Therefore, the given figure is not a triangle.

Missing angles

Example:

Find the missing angle of the given triangle Solution:

The sum of the given angles = 60° + 70° = 130°
The total angle of the triangle = 180°
Missing angle = 180° – 130 °
= 50°   • -