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f(x) àÁ××èÍ à»ÅÕ蹨ҡ x ä»à»ç¹ x + h ¤×Í hf(x+h)−f(x) «Öè§ÊÒÁÒöà¢Õ¹ä´éÍաẺ˹Öè§ ¤×Í
ÍѵÃÒ¡ÒÃà»ÅÕè¹á»Å§à©ÅÕè¢ͧ f(x) àÁ××èÍ à»ÅÕ蹨ҡ x1 ä»à»ç¹ x2 ¤×Í x2−x1f(x2)−f(x1) ÍÂèÒ§¢éÍ 1) ⨷ÂìãËéÁÒÇèÒ s(t) = 2t - 3
ÍѵÃÒ¡ÒÃà»ÅÕè¹á»Å§à©ÅÕèÂàÁ×èÍ t à»ÅÕ蹨ҡ 2 ä»à»ç¹ 2.2 ¤×Í 2.2−2s(2.2)−s(2) áµè s(2) = 2(2) - 3 áÅÐ s(2.2) = 2(2.2) - 3 àÍÒä»á·¹¤èҡ稺¤ÃѺ
ÊèǹÍѵÃÒ¡ÒÃà»ÅÕè¹¢³Ð·Õè x ã´ æ ã¹àº×éͧµé¹àÁ×èÍàÃÔèÁàÃÕ¹ ¨ÐËÒ¨Ò¡¹ÔÂÒÁ ¤×Í
limh→0hf(x+h)−f(x) «Öè§àÁ×èÍàÃÕ¹µèÍ仡ç¨ÐÒÍÍ¡ÁÒà»ç¹ÊٵáÒÃËÒ͹ؾѹ¸ì µèÒ§ æ àªè¹
dxdx=1
dxd(cx)=c
