Please can help me with three questions please I need good answer

Directions: Give complete answers to the following questions. If you choose to write out your answers by hand it must be legible. In any case, your hwk must be uploaded on Blackboard by the due date. 1. \#48 pg 128 in book Find an example of 33 matrices A and B such that AB is the 33 zero matrix, but A and B have no zero entries. 2. \#68 pg 142 in book. Let A and B be nn matrices. Prove that if A is singular then so is AB. 3. \#38 pg 177 in book. Find an example of two subspaces S1 and S2 of R3 such that S1S2 is not a subspace of R3