"This answer is not negative either."
Translation:Ez a válasz sem negatív.
What's the difference between 'sem' and 'se'? I thought they were the same thing.
There is a difference. "Se" is used in imperative sentences (commands). Its meaning is something like "don't ..., either".
Similarly, "nem" has a "ne" pair, for imperative, prohibitive sentences.
"Nem olvasom azt a könyvet." - I am not reading that book.
"Ne olvasd azt a könyvet." - Do not read that book.
"Ezt a könyvet sem olvasom." - I am not reading this book, either.
"Ezt a könyvet se olvasd." - Do not read this book, either.
In everyday speech, "sem" is often replaced by "se".