To find the surface area of a prism, we first find the areas of its ends (cross sections) an add it to the lateral area.

Surface area of prisms = 2(area of a uniform cross section) + area of lateral surface

Where; lateral surface area = perimeter of cross section * length

Ex: find the surface area of a prism whose uniform cross section is an equilateral triangle of sides 2cm and height 1.7cm and length 2cm

Solution:                     

         2cm

                                                                 1.7cm  

         2cm

Surface area of prism = area of uniform cross section + lateral section area

Area of uniform cross section = ½ * base * height = ½ (2 * 1.7) = 1.7cm²

But there are 2 ends; 2 * 1.7 = 3.4 cm²

Lateral surface area = perimeter of base * length

Perimeter of cross section = 2 + 2 + 2 = 6cm

Lateral surface area = 6 * 2 = 12cm²

Surface area of prism = 3.4 + 12 = 15.4cm²