Let A in M_m(F), be a Nilpotent matrix.
Prove the following:
1. A is a non-invertible matrix.
2. Order of nilpotentence of A small or equals to m.
3. I_n + A + A^2 +... + A^(k-1) is invertible when k is nilpotentence order of A.
4. If B is in M_n(F), a matrix. Is A+B must be Nilpotent matrix?
5. If B is in M_n(F), a matrix. Is A*B must be Nilpotent matrix?
6. Find B in M_5(R) Nilpotent matrix with order of 5.