() = ( − 2) + 4, giving asymptotic bounds
Take the first example. Start calculating T (100) = T (98) + 4 = T (96) + 4 + 4 = T (94) + 12 = T (92) + 16 ...

Seriously, that's the first thing you do. You have a problem, you try what happens. At this point it should be absolutely obvious to you what happens, right? I hope I don't have to write down the solution? 

The next one: T (100) = 3 T (99) + 3 = 9 T (98) + 9 + 3 = 9 * T (98) + 12 = 27 * T (97) + 39 = 81 * T (96) + 120 ... Slightly more complicated, but you see that one of the numbers is a power of 3, and the other one is slightly less obvious $(3^k - 3) / 2$. Figure it out from there. 

The next one: Well, I'll start with 512. T (512) = $2 T (64) +  4 * 512^2$ $2 * (2 T (8) + 4 * 64^2) + 1024^2$ = $4 T (8) + 8 * 64^2 + 4 * 512^2$ = $4 * (2 T (1) + 4 * 8^2) + 8 * 64^2 + 4 * 512^2$ = $8 T (1) + 8 * 8^2 + 8 * 64^2 + 4 * 512^2$ - it should be clear what the dominating factor is in this equation. 

This is all mathematically trivial. All you had to do to solve these problems is to not look at them and be stunned by the strange formulas but having a go and starting to calculate and see what happens. 

PS. The answer was intended to demonstrate that seemingly hard problems can often be attacked quite easily, that overcoming your fear of the unknown and jumping in and seeing what happens is often enough. That is much, much more important than solving one particular problem. You may call this a "waste of time", but I Don't Think So. 

The quoted "reference answer" may answer the question, but doesn't inspire anyone to try finding the answer themselves.