Answer
Find out the what is the surface area of the pyramid .
To proof
Formula
Surface area of a square pyramid
Where a is the base edge and h be the height .
As given
A square pyramid has a base with side lengths each measuring 40 inches. The pyramid is 21 inches tall, with a slant height of 29 inches.
i.e Base edge = 40 inches
Height = 21 inches
Put values in the above formula
solving
= 1600 + 80 × 29
= 3920 inches²
Therefore the surface area of the pyramid is 3,920 inches²
Hence proved