點解integral可以用黎搵面積?

因為是證明出來的。

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參考資料：
http://hk.knowledge.yahoo.com/question/question?qid=7008040101472

我地將個function 既under area 想像成由好多條長方體所組成,say n , 每個長方體都係equal width, 最後將n take limit .



http://en.wikipedia.org/wiki/Riemann_integral