定義
![無窮小量](/img/0/bc2/wZwpmL0YTM5QTN0YTMxMzM1UTM1QDN5MjM5ADMwAjMwUzL2EzL3MzLt92YucmbvRWdo5Cd0FmLzE2LvoDc0RHa.jpg)
![無窮小量](/img/5/151/wZwpmL1gTM5cDO2YTMzEzM1UTM1QDN5MjM5ADMwAjMwUzL2EzL1UzLt92YucmbvRWdo5Cd0FmLxE2LvoDc0RHa.jpg)
![無窮小量](/img/5/151/wZwpmL1gTM5cDO2YTMzEzM1UTM1QDN5MjM5ADMwAjMwUzL2EzL1UzLt92YucmbvRWdo5Cd0FmLxE2LvoDc0RHa.jpg)
無窮小是極限為零的函式。如是自變數,因變數極限為零的函式。此時f(x)就是的無窮小。
無窮大是指絕對值大於任何數的函式,因此負無窮不是無窮小,而是無窮大。
![無窮小量](/img/8/3c3/wZwpmLzQTN2QjM3cDOxMzM1UTM1QDN5MjM5ADMwAjMwUzL3gzLxQzLt92YucmbvRWdo5Cd0FmLzE2LvoDc0RHa.jpg)
設f在某x的空心鄰域有定義。
![無窮小量](/img/d/23e/wZwpmLxATO4EzMxMTMzEDN0UTMyITNykTO0EDMwAjMwUzLzEzLyIzLt92YucmbvRWdo5Cd0FmLxE2LvoDc0RHa.jpg)
![無窮小量](/img/0/a26/wZwpmL1MDO4YjM5cTO4kzM0UTMyITNykTO0EDMwAjMwUzL3kzL3IzLt92YucmbvRWdo5Cd0FmLyE2LvoDc0RHa.jpg)
![無窮小量](/img/d/2a0/wZwpmLzATO2YTO3EDMyMzM1UTM1QDN5MjM5ADMwAjMwUzLxAzLxQzLt92YucmbvRWdo5Cd0FmLzE2LvoDc0RHa.jpg)
![無窮小量](/img/f/f01/wZwpmLwATOyUTM4ADOxMzM1UTM1QDN5MjM5ADMwAjMwUzLwgzLxIzLt92YucmbvRWdo5Cd0FmLwE2LvoDc0RHa.jpg)
![無窮小量](/img/1/036/wZwpmL3QzM5YjNzMjM0EDN0UTMyITNykTO0EDMwAjMwUzLzIzL3EzLt92YucmbvRWdo5Cd0FmLwE2LvoDc0RHa.jpg)
![無窮小量](/img/b/cd4/wZwpmLxcTNyUjNwMDO4EDN0UTMyITNykTO0EDMwAjMwUzLzgzLzIzLt92YucmbvRWdo5Cd0FmLwE2LvoDc0RHa.jpg)
![無窮小量](/img/8/31c/wZwpmL1gDOzQzMyAjNwMzM1UTM1QDN5MjM5ADMwAjMwUzLwYzL3EzLt92YucmbvRWdo5Cd0FmLxE2LvoDc0RHa.jpg)
![無窮小量](/img/b/cd4/wZwpmLxcTNyUjNwMDO4EDN0UTMyITNykTO0EDMwAjMwUzLzgzLzIzLt92YucmbvRWdo5Cd0FmLwE2LvoDc0RHa.jpg)
![無窮小量](/img/5/151/wZwpmL1gTM5cDO2YTMzEzM1UTM1QDN5MjM5ADMwAjMwUzL2EzL1UzLt92YucmbvRWdo5Cd0FmLxE2LvoDc0RHa.jpg)
![無窮小量](/img/0/7f3/wZwpmL1UjNzgzN1ATOxADN0UTMyITNykTO0EDMwAjMwUzLwkzL3YzLt92YucmbvRWdo5Cd0FmLzE2LvoDc0RHa.jpg)
![無窮小量](/img/0/bc2/wZwpmL0YTM5QTN0YTMxMzM1UTM1QDN5MjM5ADMwAjMwUzL2EzL3MzLt92YucmbvRWdo5Cd0FmLzE2LvoDc0RHa.jpg)
![無窮小量](/img/4/7ab/wZwpmL0gzMyUTMwgzNxMzM1UTM1QDN5MjM5ADMwAjMwUzL4czLwgzLt92YucmbvRWdo5Cd0FmL0E2LvoDc0RHa.jpg)
對於任給的正數 ε(無論它多么小),總存在正數 (或正數 )使得不等式(或 )的一切 對應的函式值 都滿足不等式 ,則稱函式 為當 (或 )時的無窮小量。記做: (或 )。
性質
1、無窮小量不是一個數,它是一個變數。
2、零可以作為無窮小量的唯一一個常量。
3、無窮小量與自變數的趨勢相關。
![無窮小量](/img/8/36b/wZwpmLycTN3YDNxkjNwMzM1UTM1QDN5MjM5ADMwAjMwUzL5YzL4AzLt92YucmbvRWdo5Cd0FmLyE2LvoDc0RHa.jpg)
![無窮小量](/img/d/58f/wZwpmLyEjN4ITNyMTMzEDN0UTMyITNykTO0EDMwAjMwUzLzEzLxczLt92YucmbvRWdo5Cd0FmL0E2LvoDc0RHa.jpg)
![無窮小量](/img/5/151/wZwpmL1gTM5cDO2YTMzEzM1UTM1QDN5MjM5ADMwAjMwUzL2EzL1UzLt92YucmbvRWdo5Cd0FmLxE2LvoDc0RHa.jpg)
4、若函式 在某 的空心鄰域內有界,則稱g為當 時的有界量。
![無窮小量](/img/d/1b5/wZwpmLyEDN0UjM5YzNxMzM1UTM1QDN5MjM5ADMwAjMwUzL2czL4czLt92YucmbvRWdo5Cd0FmLwE2LvoDc0RHa.jpg)
![無窮小量](/img/2/a78/wZwpmL4YDM5ITN3EzMzEzM1UTM1QDN5MjM5ADMwAjMwUzLxMzLyEzLt92YucmbvRWdo5Cd0FmLwE2LvoDc0RHa.jpg)
![無窮小量](/img/c/af5/wZwpmL1cTN2cDNyczNwMzM1UTM1QDN5MjM5ADMwAjMwUzL3czL1QzLt92YucmbvRWdo5Cd0FmLwE2LvoDc0RHa.jpg)
![無窮小量](/img/3/c9a/wZwpmL2YzM5IjM4czNwMzM1UTM1QDN5MjM5ADMwAjMwUzL3czL3QzLt92YucmbvRWdo5Cd0FmLzE2LvoDc0RHa.jpg)
![無窮小量](/img/0/eab/wZwpmL4ITN5UTM2AzNwMzM1UTM1QDN5MjM5ADMwAjMwUzLwczLwMzLt92YucmbvRWdo5Cd0FmLxE2LvoDc0RHa.jpg)
![無窮小量](/img/0/7f3/wZwpmL1UjNzgzN1ATOxADN0UTMyITNykTO0EDMwAjMwUzLwkzL3YzLt92YucmbvRWdo5Cd0FmLzE2LvoDc0RHa.jpg)
![無窮小量](/img/c/854/wZwpmLzADO3QDM5QTOwMzM1UTM1QDN5MjM5ADMwAjMwUzL0kzL2AzLt92YucmbvRWdo5Cd0FmLxE2LvoDc0RHa.jpg)
![無窮小量](/img/2/a78/wZwpmL4YDM5ITN3EzMzEzM1UTM1QDN5MjM5ADMwAjMwUzLxMzLyEzLt92YucmbvRWdo5Cd0FmLwE2LvoDc0RHa.jpg)
例如 ,都是當 時的無窮小量, 是當 時的無窮小量,而 為 時的有界量, 是當 時的有界量。特別的,任何無窮小量也必定是有界量。
5、有限個無窮小量之和仍是無窮小量。
6、有限個無窮小量之積仍是無窮小量。
7、有界函式與無窮小量之積為無窮小量。
8、特別地,常數和無窮小量的乘積也為無窮小量。
9、恆不為零的無窮小量的倒數為無窮大,無窮大的倒數為無窮小。
無窮大
![無窮小量](/img/b/cd4/wZwpmLxcTNyUjNwMDO4EDN0UTMyITNykTO0EDMwAjMwUzLzgzLzIzLt92YucmbvRWdo5Cd0FmLwE2LvoDc0RHa.jpg)
![無窮小量](/img/5/151/wZwpmL1gTM5cDO2YTMzEzM1UTM1QDN5MjM5ADMwAjMwUzL2EzL1UzLt92YucmbvRWdo5Cd0FmLxE2LvoDc0RHa.jpg)
![無窮小量](/img/6/e13/wZwpmL2AjN0IzN1gjNwMzM1UTM1QDN5MjM5ADMwAjMwUzL4YzL3gzLt92YucmbvRWdo5Cd0FmLzE2LvoDc0RHa.jpg)
當自變數x趨於x時,函式的絕對值無限增大,則稱 為當 時的無窮大。記作 。
同樣,無窮大不是一個具體的數字,而是一個無限發展的趨勢。
階的比較
前提條件
無窮小量是以0為極限的函式,而不同的無窮小量收斂於0的速度有快有慢。因此兩個無窮小量之間又分為高階無窮小 ,低階無窮小,同階無窮小,等價無窮小。
![無窮小量](/img/f/8c2/wZwpmLwADN2UzM5IjNwMzM1UTM1QDN5MjM5ADMwAjMwUzLyYzL1MzLt92YucmbvRWdo5Cd0FmLyE2LvoDc0RHa.jpg)
![無窮小量](/img/5/151/wZwpmL1gTM5cDO2YTMzEzM1UTM1QDN5MjM5ADMwAjMwUzL2EzL1UzLt92YucmbvRWdo5Cd0FmLxE2LvoDc0RHa.jpg)
![無窮小量](/img/9/ce6/wZwpmLyATN5UjM4QTOwADN0UTMyITNykTO0EDMwAjMwUzL0kzL1AzLt92YucmbvRWdo5Cd0FmL0E2LvoDc0RHa.jpg)
![無窮小量](/img/d/58f/wZwpmLyEjN4ITNyMTMzEDN0UTMyITNykTO0EDMwAjMwUzLzEzLxczLt92YucmbvRWdo5Cd0FmL0E2LvoDc0RHa.jpg)
首先規定 都為 時的無窮小, 在某 的空心鄰域恆不為0。
高低階無窮小量
![無窮小量](/img/d/195/wZwpmLxQzNxUTM3gzMxMzM1UTM1QDN5MjM5ADMwAjMwUzL4MzL0MzLt92YucmbvRWdo5Cd0FmL0E2LvoDc0RHa.jpg)
![無窮小量](/img/5/151/wZwpmL1gTM5cDO2YTMzEzM1UTM1QDN5MjM5ADMwAjMwUzL2EzL1UzLt92YucmbvRWdo5Cd0FmLxE2LvoDc0RHa.jpg)
,則稱當 時,f為g的高階無窮小量,或稱g為f的低階無窮小量。
![無窮小量](/img/2/503/wZwpmL1gDO0cTN3gjNxMzM1UTM1QDN5MjM5ADMwAjMwUzL4YzLzUzLt92YucmbvRWdo5Cd0FmLxE2LvoDc0RHa.jpg)
![無窮小量](/img/5/151/wZwpmL1gTM5cDO2YTMzEzM1UTM1QDN5MjM5ADMwAjMwUzL2EzL1UzLt92YucmbvRWdo5Cd0FmLxE2LvoDc0RHa.jpg)
記做 ( )
![無窮小量](/img/5/151/wZwpmL1gTM5cDO2YTMzEzM1UTM1QDN5MjM5ADMwAjMwUzL2EzL1UzLt92YucmbvRWdo5Cd0FmLxE2LvoDc0RHa.jpg)
![無窮小量](/img/e/645/wZwpmL0MTM2YTNzYzNwMzM1UTM1QDN5MjM5ADMwAjMwUzL2czL4UzLt92YucmbvRWdo5Cd0FmLwE2LvoDc0RHa.jpg)
![無窮小量](/img/5/151/wZwpmL1gTM5cDO2YTMzEzM1UTM1QDN5MjM5ADMwAjMwUzL2EzL1UzLt92YucmbvRWdo5Cd0FmLxE2LvoDc0RHa.jpg)
特別的,f為當 時的無窮小量記作 ( )。
同階無窮小量
![無窮小量](/img/1/13d/wZwpmL0ATNygDO5QDOwMzM1UTM1QDN5MjM5ADMwAjMwUzL0gzL2EzLt92YucmbvRWdo5Cd0FmLzE2LvoDc0RHa.jpg)
![無窮小量](/img/5/151/wZwpmL1gTM5cDO2YTMzEzM1UTM1QDN5MjM5ADMwAjMwUzL2EzL1UzLt92YucmbvRWdo5Cd0FmLxE2LvoDc0RHa.jpg)
當 (c≠0)時,ƒ和ɡ為 時的同階無窮小量。
當x→0時的同階無窮小量:
![無窮小量](/img/d/4e6/wZwpmL3QTM4YjM1gzMxMzM1UTM1QDN5MjM5ADMwAjMwUzL4MzL4gzLt92YucmbvRWdo5Cd0FmL0E2LvoDc0RHa.jpg)
![無窮小量](/img/7/21a/wZwpmL1ATN2gzN1kTOxMzM1UTM1QDN5MjM5ADMwAjMwUzL5kzLyAzLt92YucmbvRWdo5Cd0FmLwE2LvoDc0RHa.jpg)
與
![無窮小量](/img/0/f24/wZwpmL2gDO5EDN1QTOwMzM1UTM1QDN5MjM5ADMwAjMwUzL0kzL3QzLt92YucmbvRWdo5Cd0FmL0E2LvoDc0RHa.jpg)
![無窮小量](/img/f/354/wZwpmL2UTO3kzM0YTOxMzM1UTM1QDN5MjM5ADMwAjMwUzL2kzLxMzLt92YucmbvRWdo5Cd0FmLwE2LvoDc0RHa.jpg)
與
等價無窮小量
![無窮小量](/img/2/5cf/wZwpmL2UTNyMjN1gjMzEzM1UTM1QDN5MjM5ADMwAjMwUzL4IzL2AzLt92YucmbvRWdo5Cd0FmL0E2LvoDc0RHa.jpg)
![無窮小量](/img/5/151/wZwpmL1gTM5cDO2YTMzEzM1UTM1QDN5MjM5ADMwAjMwUzL2EzL1UzLt92YucmbvRWdo5Cd0FmLxE2LvoDc0RHa.jpg)
![無窮小量](/img/8/830/wZwpmLwQDM1YTNycDOyYDM1UTM1QDN5MjM5ADMwAjMwUzL3gzLyczLt92YucmbvRWdo5Cd0FmLwE2LvoDc0RHa.jpg)
![無窮小量](/img/5/151/wZwpmL1gTM5cDO2YTMzEzM1UTM1QDN5MjM5ADMwAjMwUzL2EzL1UzLt92YucmbvRWdo5Cd0FmLxE2LvoDc0RHa.jpg)
,則稱ƒ和ɡ是當 時的等價無窮小量,記做: ( )。
等價無窮小量套用最廣泛,常見的有:
當x→0時
![無窮小量](/img/b/825/wZwpmL1czMzETN3QTOwMzM1UTM1QDN5MjM5ADMwAjMwUzL0kzL1IzLt92YucmbvRWdo5Cd0FmL0E2LvoDc0RHa.jpg)
![無窮小量](/img/9/a58/wZwpmL3cTNzgTNyIzNxMzM1UTM1QDN5MjM5ADMwAjMwUzLyczLwYzLt92YucmbvRWdo5Cd0FmLwE2LvoDc0RHa.jpg)
![無窮小量](/img/c/bb8/wZwpmL2gzNwATO5YTOxMzM1UTM1QDN5MjM5ADMwAjMwUzL2kzLxczLt92YucmbvRWdo5Cd0FmLwE2LvoDc0RHa.jpg)
![無窮小量](/img/2/a78/wZwpmL4YDM5ITN3EzMzEzM1UTM1QDN5MjM5ADMwAjMwUzLxMzLyEzLt92YucmbvRWdo5Cd0FmLwE2LvoDc0RHa.jpg)
, , ( )