Question 31
The surface area of a cuboid formed by joining two cubes of side a face-to-face, is
10a2
We have, two cubes of side a.
These two cubes are joined face-to-face, then the resultant solid figure is a cuboid which has same breadth and height as the joined cubes has length twice of the length of a cube.
i.e. l = 2a, b = a and h = a
Thus, the total surface area of the cuboid =2(lb+bh+hl)
=2(2a×a+a×a+a×2a)=2(2a2+a2+2a2)=2×5a2=10a2