I'm just getting started as an amateur into microeconomics and I really can't understand this thing about marginal utility when more than one good is involved:
Let's say I have the utility function U = x(y+1).
Now, from what I've studied, I think that the marginal utilities for x and y should be:
MUx = y+1
MUy = x
I just don't get how to arrive there "mathematically", and I fear I wouldn't be able to find the marginal utilities of a more complex function, for example U = x(x+y)
Could you help me?