Matrices revision

Matrices of any order can be added.

The number of matrices having 7 elements is……………

show that the product of two triangular matrices is itself triangular

Find the number of matrices having 12 elements

Let A,B and C be nxxn matrices. Which one of the following is a correct statement?

If [(lambda^(2)-2lambda+1,lambda-2),(1-lambda^(2)+3lambda,1-lambda^(2))]=Alambda^(2)+Blambda+C , where A, B and C are matrices then find matrices B and C.

If A and B are symmetric matrices, then ABA is