Triangles - Orchids The International School
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Geometry

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.
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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.

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Isosceles Triangle

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

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Scalene Triangle

In a scalene triangle, the length of all the sides of the triangle is unequal.

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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:

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Angles in Triangle

  • There are three angles in a triangle.
  • The sum of the angles of a triangle is equal to 180°.
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The sum of the angle = 45° + 90° + 45° = 180°
Therefore, the given figure is a triangle.

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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

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Solution:

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

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