I'm taking mechanics and my professor said that the upcoming test will be very similar to the homework problems assigned. But he said we should know how to work the problems backwards. So in the homework he gives us a and b and we have to solve for c and he's saying that on the test he will change it up so that we have b and c but not a. What i want to do is change the homework problems myself so I can get used to solving the problems in every way. How would I go about doing this? To reverse a problem that has 3 knowns and 2 unknowns, would it be safe to say that if i started with the 2 uknowns, then i should be able to solve for the other three?