If you cut squares which are s x s in each corner, then fold up the flaps to make a box, then

- the height of the box is s
- the bottom of the box is (10 - 2s) x (8 - 2s) because you've taken 2s from each side.

So V = s(10-2s)(8 - 2s)

Multiply that out. Take the derivative with respect to s. Set it equal to 0.

View the original article here