Jonathan Andres S.
Thanks a lot. There must be a mistake in the exercise then, I agree with your answer. I don't understand how can you affirm #(x+y)^(mn)=x^m y^n#? Can you explain it briefly please?
Integration (as with differentiation) is unique (with the exception of constant). So if you get two solutions there are two possible inferences: (1) you made a mistake or (2) the two solutions are equivalent.