Linear Algebra

Please list whether the following is True or False:

(8) If u and v are solutions to Ax 0, then u v is a solution to Ax0 (9) If u an v are solutions to Ax = b, then u-v is also a solution to Ax 0 (10) A given matrix can have different echelon forms (11) Suppose that linear system Ax b is consistent. Then the number of basic variables of Ax-b is the same as the number of pivot positions of matrix A. (12) If p is a solution to Ax b and u is a solution to Ax 0, then up is a solution to Ax h. 13) Some elementary matrices are not invertible. (14) If A and B are invertible, the AB is also invertible. (15) If A is an invertible matrix, then AB = 0 implies B-0