Let E be the elementary matrix E₂ of Example 6 and suppose that A is a 3 x 3 matrix. Show that EA is the result upon adding twice the first row of A to its third row.

Example 6

Example 6 We obtain some typical elementary matrices as follows. 1 0 0 1 0 [9] 0 1 0 0 0 1 0 1 001 0 0 (3) R (2) R + R3 SWAP(R, R) [3]= 1 0 2 = E 0 0 1 0 0 1 0 1 0 10 0 0 01 = E =E3 The three elementary matrices E, E2, and E3 correspond to three typical elementary row operations. Now, suppose that the mxm elementary matrix E corresponds to a certain elementary row operation. It turns out that if we perform this same operation on an arbitrary mxn matrix A, we get the product matrix EA that results upon multiplying A on the left by the matrix E. Thus we can carry out an elementary row operation by means of left multiplication by the corresponding elementary matrix. Problems 38-40 illustrate typical cases in the proof of the following theorem.