[微積] 幾題證明

[KOREALee (韓國最高)]

1.use the definition of the limit to show that

       1
 lim ----- = 0
x→∞  x


2.show that if  d^2/dx^2 f(x)>0 , then f(x) is concave upward


3.show that if  d^2/dx^2 f(x)<0 , then f(x) is concave downward



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