what is diagonal

In geometry, a diagonal is a line segment that joins two vertices of a polygon or polyhedron, when those vertices are not on the same edge. In other words, a diagonal is a line that connects two non-adjacent vertices of a polygon. The word diagonal derives from the ancient Greek διαγώνιος diagonios, "from angle to angle". The diagonal of a square matrix in matrix algebra consists of the entries on the line from the top left corner to the bottom right corner. In engineering, a diagonal brace is a beam used to brace a rectangular structure (such as scaffolding) to withstand strong forces pushing into it.