SURFACE AREA OF PYRAMID WITH TRIANGULAR BASE

Pyramid is basically a 3D shape. Even though we have formulas to find surface area of pyramid with triangular base, the basic idea of finding surface is to add the areas of all the faces.  

To understand how to find surface area of a pyramid with triangular base, let us consider the pyramid given below.

For any pyramid, if the shape of the base is equilateral  triangle, then we will have three side walls. The shape of each side wall will be a triangle with equal area.  

In the above pyramid, the base is an equilateral triangle with side length "a". 

And each wall is a triangle with base "a" and height "h"

Let us find the area of each face separately. 

Area of the base  =  (√3/4)a²

Area of each side wall  =  (1/2)ah 

Area of all 3 side walls  =  3 x (1/2)ah  =  (3/2)ah 

Surface area of the above pyramid is

=  (√3/4)a² + (3/2)ah

This is the formula to find surface area of a pyramid with equilateral triangle base. 

Note :

If the base is not equilateral triangle and it is either scalene triangle or isosceles triangle, then the area of side walls will not be equal. We have to find area of each side wall separately.  

Practice Problems

Problem 1 : 

Find the surface area of the pyramid shown below.

Solution : 

Surface area of the pyramid is

=  Sum of areas of all 4 faces

In the above pyramid, the base is an equilateral triangle with side length 4 cm and each wall is a triangle with base 4 cm and height 6 cm.

Let us find the area of each face separately. 

Area of the base  =  (√3/4) x 4²  =  4√3 sq.cm

Area of each side wall  =  (1/2) x 4 x 6  =  12 sq.cm 

Area of all 3 side walls  =  3 x 12  =  36 sq.cm 

Surface area of the above pyramid is 

=  4√3 + 36

=  4(√3 + 9)  sq. cm

Problem 2 :

Find the surface area of the pyramid shown below.

Solution : 

Surface area of the pyramid is

=  Sum of areas of all 4 faces

In the above pyramid, the base is an equilateral triangle with side length 6 cm and each wall is a triangle with base 6 cm and height 10 cm.

Let us find the area of each face separately. 

Area of the base  =  (√3/4) x 6²  =  9√3 sq.cm

Area of each side wall  =  (1/2) x 6 x 10  =  30 sq.cm 

Area of all 3 side walls  =  3 x 30  =  90 sq.cm 

Surface area of the above pyramid is

=  (9√3 + 90)

=  9(√3 + 10)  sq.cm

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