You have a brick of parallelepiped shape. You need to measure its diagonal (a distance between two opposite vertexes remote to the maximum). You have in your disposition a ruler and a rectangular edge of the plane surface (of the table, for example). What should you do to measure the diagonal if
1. You have also a pencil to make marks on the edge of the table.
2. You don't have a pencil but have another identical brick (of the same shape and dimensions).