1. 極限
簡單的極限,我們可以通過直接代入法求解,如:
我們知道我們在利用極限求導數時:
如果直接用代入法的話,會出現分母爲0的情況。
2. 連續
連續的定義:
We say
f(x) is continuous atx0 when
limx→x0f(x)=f(x0)
四類不連續點
1. Removable Discontinuity
Right-hand limit:
Left-hand limit:
If
limx→x+0f(x)=limx→x−0f(x) but this is notf(x0) , or iff(x0) is undefined, we say the discontinuity isremovable
.
比如說
2. Jump Discontinuity
limx→x+0f(x) for(x<x0 ) exists, andlimx→x−0f(x) for(x>x0 )also exists, but they are NOT equal.
3. Infinite Discontinuity
Right-hand limit:
Left-hand limit:
4. Other(Ugly) discontinuity
This function doesn’t even go to
±∞ — it doesn’t make sense to say it goes to anything. For something like this, we say the limit does not exist.
3. 兩個三角函數的極限
注意下面的表達式中
幾何證明:
當上圖中的角度
從上圖中可以看出當角度變得越來越小時,
4. 定理:可微則一定連續
If
f is differentiable atx0 , thenf is continuous atx0 .
Proof: