As tkhunny said, the basic way to prove each of these is to use separate cases. The first three will be similar: show that it is true for all x >= 0,...
Hi. Sure someone here can help. That is never a problem. But 1st you need to tell us where you are stuck or what you have tried and then once we see...
I see that you are still practicing your times table as I suggested. Good job. One day you will get beyond the 5 table. Just keep trying, I know you...