Question

Help please??

Answer 1

We know that the surface area is the sum of the areas of all the surfaces. We start by seeing that the area of the square base is simply `x^2`.

The height of the triangles will be `(20 - x)/2`. The area of the triangles will therefore be

`A_Delta= ((x(20 - x))/2)/2 * 4` (as there are 4 triangles)

`A_Delta = (x(20 - x))/4 * 4`

`A_Delta =`x(20 - x)#

`A_Delta = 20x - x^2`

Now simply add this to the area of the square

`A_"pyramid" = x^2 + 20x - x^2 = 20x`

As required.

Hopefully this helps!