Question

What is the identity matrix of size 4?

Answer 1

The identity matrix of a 4x4 matrix is:

`((1,0,0,0),(0,1,0,0),(0,0,1,0),(0,0,0,1))`

To find the identity matrix of an nxn matrix you simply put 1's for the main diagonal (from the top left to the bottom right http://en.wikipedia.org/wiki/Main_diagonal) of the matrix, and zeroes everywhere else (so in the "triangles" below and above the diagonals)