"Proof needed"

Sometimes the problem with teaching is that the concept can be alien. And thus, some people feel that they need clarification on topics you took for granted.

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And when you get stuff like "Proof needed" in your sample answers you feel like punching the person who gave the answers in the first place. Why the hell bother to give answers if you can't tell us how you arrive at the "proof"?

Anyhow, back to studying. Getting bashed by my friends for not doing much for calculus now.