Is there a system or equation to opening/cracking a lock (padlock, bike lock, or other)?

I have a used bike lock and i don't know the combination!

It depends on the lock, but there could be anywhere from a few hundred to a hundred thousand possible combinations. The only system to finding the right one is something like 1-1-1, 1-1-2,1-1-3... Cutting the lock will be a lot faster.

yes justlisten for the clix and use the same turning patern

Yes, one turn to the right and stop on 0. Two turns to the left and stop on 0. Three turns to the right and stop on 0 and cut the stupid thing off with a set of bolt cutters!

go to a welder, so they can cut it off...
get a new one and write down the combination...

It's probably not worth the effort, but you could try this. Pull on both ends of the lock, and keep them tense during the process. The lock will hold itself together by the 3 or 4 combination wheels. While pulling on both ends (you might need a foot and a hand for this) find the combination wheel that is harder to move. If you find one that puts more resistance than the others, rotate that one until you feel a change, as if it just let go a little bit. When it happens, repeat the process with the remaining wheels. Rinse and repeat. If the lock is el-cheapo type, you'll get it right in a couple of minutes. If it is a finely machined padlock, this will not work. Hope this helps.