Eight vertices of a cube are indicated by the eight letters – A through H. Each letter is associated with an adjacent dot, but it is ambiguous which letter goes with which dot due to their respective proximities.
Only two dots are clearly assigned – the upper right and the lower left ones. They are lettered with C and G respectively, since those dots are not adjacent to any other letters.
To assign the letters without any ambiguity, the following relation is true: DH > EG > AB.
Which one of the provided equations is not correct?
In a cube only three different segments can be obtained between any two vertices, from bigger to smaller: a cube’s diagonal, a face’s diagonal, and the cube’s edge, which in our case are DH, EG, and AB respectively.
Based on this, the letters are then assigned as is shown in the diagram. Based on the assignment, the equation AB = DE is not correct since AB is the edge, while DE is the face’s diagonal.