$x_1 + x_2 + x_3 + x_4 = 28$ I tried to solve it with generating functions. Is it correct to get to the form of ${(1 + x + {x^2} + {x^3} + ....)^4}$ and this equals to: ${(1 - x)^{ - 4}}$ and then solve it with binomial expansion ? Is this correct ? every question similar to "how many solutions are axsist to this equation?" can be solved this method? I know there're a lot of methods and manipulations for this kind of problem. Can you confirm it's the right path for this kind of problems? It's like distribute 28 things into 4 objects. This is why I used generating functions.
