In geometry, you have various kinds of shapes and you have equations that help you to determine the perimeter and area of the shapes easily. In this section, we will look at how to calculate the perimeter and areas of different shapes.
Perimeter of a Shape
A rectangle is 4-sided shape where all the angles of the shapes equal 90°. But the adjacent sides of a rectangle are not equal in length.
Now the perimeter of a shape the distance around the outside of the shape. In the case of a rectangle, the perimeter is the sum of the length of all the 4 sides.
So, when you calculate the perimeter of the rectangle above, you write it like this:
Perimeter of Rectangle = 7 + 3 + 7 + 3 = 20 cm
The formula to calculate the perimeter of a rectangle is 2 (l + b), where l is length and b is breadth.
So, when you apply the formula here:
Perimeter of Rectangle = 2 (7 + 3) = 20 cm
Now let’s look at the triangle above. The perimeter of a triangle is the sum of the length of all the three sides. To calculate the perimeter of the triangle above, simply add the side lengths.
Perimeter of Triangle = 12 + 10 + 8 = 20 cm
The formula to calculate the perimeter of a triangle is a + b + c, where a, b and c are the length of the three sides of a triangle.
So, when you apply the formula here, it looks like this:
Perimeter of Triangle = (12 + 10 + 8) = 20 cm
Area of Shapes
Area is the amount of a two-dimensional space of a shape. The area of a rectangle is nothing but the length of the rectangle multiplied by the width of the rectangle.
Now let’s calculate the area of the rectangle shown above:
Area of Rectangle = 7 x 3 = 21 cm
The formula to calculate is l x b, where l is length and b is breadth.
But when you want to calculate the area of a triangle, you need to multiply the height of the triangle with only half the length of the base.
Now let’s calculate the area of the triangle shown above:
Area of Triangle = ½ x 10 x 8 = 40 cm
Below is a table of the formulas for perimeter and area of common 2-D shapes.