Which of the following subsets of R3 Times 3are subspaces of

Which of the following subsets of R^3 Times 3|are subspaces of R^3 Times 3|? The 3 Times 3| matrices with determinant 0| The 3 Times 3| matrices whose entries are all greater than or equal to 0| The invertible 3 Times 3| matrices The symmetric 3 Times 3| matrices The diagonal 3 Times 3| matrices The 3 Times 3| matrices with all zeros in the third row

Solution

The diagonal 3X3 matrices