A triangle is a polygon with 3 sides and 3 vertices.

**Types of Triangles**

Depending on the length of the sides of the triangle and the interior angles of a triangle, triangles can be of different types.

Based on length of sides, triangles can be classified as equilateral, isosceles or scalene triangles.

Based on measure of angles, triangles can be classified as right angled, obtuse angled or acute angled triangles.

**Perimeter of a triangle**

The perimeter is defined as the distance around a two dimensional shape. For a polygon, the perimeter is equal to the sum of the sides of the polygon. In case of a triangle, the perimeter is given by the formula

Perimeter = a + b + c

Where a, b and c are the length of the three sides of the triangle respectively.

**Practice questions:**

Question: Calculate the perimeter of a triangle with length equal to 6 cms, 4 cms and 2 cms.

( Answer: Perimeter of the triangle = sum of the lengths of the 3 sides

= 6 + 4 + 2

= 12 cms

)

Question: Calculate the perimeter of an equilateral triangle with length of one of the sides equal to 5 cms.

( Answer: Perimeter of the triangle = sum of the lengths of the 3 sides

= 5 + 5 + 5 ( as all 3 sides are equal )

= 15 cms

)

**Area of the triangle**

The area of a triangle is given by the formula

Area = ½ * b * h

Where b is the length of the base of the triangle and h is the height of the triangle.

The area of the triangle is measured in sq cms.

**Practice questions:**

Question: Find the area of a triangle with base equal to 2 cms and height equal to 4 cms.

( Answer: Base of the triangle b = 2 cms

Height of the triangle h = 4 cms

Area of the triangle = ½ * 2 * 4

= 4 sq cms

)

Question: Find the area of a triangle whose base is equal to 4 cms and whose height is equal to 3 cms.

( Answer: Base of the triangle b = 4 cms

Height of the triangle h = 3 cms

Area of the triangle = ½ * 4 * 3

= 6 sq cms

)

Question: The area of a triangle is 20 sq cms. If the height of triangle is 8 cms, what is the length of the base of the triangle.

( Answer: Area of the triangle = 20 sq cms

Height of the triangle h = 8 cms

20 = ½ * b * 8

Base of the triangle b = 5 cms

)

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