數學基礎知識
數據科學需要一定的數學基礎,但僅僅做應用的話,如果時間不多,不用學太深,瞭解基本公式即可,遇到問題再查吧。
下面是常見的一些數學基礎概念,建議大家收藏後再仔細閱讀,遇到不懂的概念可以直接在這裏查~
高等數學
1.導數定義:
導數和微分的概念
f ′ ( x 0 ) = lim Δ x → 0 f ( x 0 + Δ x ) − f ( x 0 ) Δ x f'({{x}_{0}})=\underset{\Delta x\to 0}{\mathop{\lim }}\,\frac{f({{x}_{0}}+\Delta x)-f({{x}_{0}})}{\Delta x} f ′ ( x 0 ) = Δ x → 0 lim Δ x f ( x 0 + Δ x ) − f ( x 0 ) (1)
或者:
f ′ ( x 0 ) = lim x → x 0 f ( x ) − f ( x 0 ) x − x 0 f'({{x}_{0}})=\underset{x\to {{x}_{0}}}{\mathop{\lim }}\,\frac{f(x)-f({{x}_{0}})}{x-{{x}_{0}}} f ′ ( x 0 ) = x → x 0 lim x − x 0 f ( x ) − f ( x 0 ) (2)
2.左右導數導數的幾何意義和物理意義
函數f ( x ) f(x) f ( x ) 在x 0 x_0 x 0 處的左、右導數分別定義爲:
左導數:f ′ − ( x 0 ) = lim Δ x → 0 − f ( x 0 + Δ x ) − f ( x 0 ) Δ x = lim x → x 0 − f ( x ) − f ( x 0 ) x − x 0 , ( x = x 0 + Δ x ) {{{f}'}_{-}}({{x}_{0}})=\underset{\Delta x\to {{0}^{-}}}{\mathop{\lim }}\,\frac{f({{x}_{0}}+\Delta x)-f({{x}_{0}})}{\Delta x}=\underset{x\to x_{0}^{-}}{\mathop{\lim }}\,\frac{f(x)-f({{x}_{0}})}{x-{{x}_{0}}},(x={{x}_{0}}+\Delta x) f ′ − ( x 0 ) = Δ x → 0 − lim Δ x f ( x 0 + Δ x ) − f ( x 0 ) = x → x 0 − lim x − x 0 f ( x ) − f ( x 0 ) , ( x = x 0 + Δ x )
右導數:f ′ + ( x 0 ) = lim Δ x → 0 + f ( x 0 + Δ x ) − f ( x 0 ) Δ x = lim x → x 0 + f ( x ) − f ( x 0 ) x − x 0 {{{f}'}_{+}}({{x}_{0}})=\underset{\Delta x\to {{0}^{+}}}{\mathop{\lim }}\,\frac{f({{x}_{0}}+\Delta x)-f({{x}_{0}})}{\Delta x}=\underset{x\to x_{0}^{+}}{\mathop{\lim }}\,\frac{f(x)-f({{x}_{0}})}{x-{{x}_{0}}} f ′ + ( x 0 ) = Δ x → 0 + lim Δ x f ( x 0 + Δ x ) − f ( x 0 ) = x → x 0 + lim x − x 0 f ( x ) − f ( x 0 )
3.函數的可導性與連續性之間的關係
Th1: 函數f ( x ) f(x) f ( x ) 在x 0 x_0 x 0 處可微⇔ f ( x ) \Leftrightarrow f(x) ⇔ f ( x ) 在x 0 x_0 x 0 處可導
Th2: 若函數在點x 0 x_0 x 0 處可導,則y = f ( x ) y=f(x) y = f ( x ) 在點x 0 x_0 x 0 處連續,反之則不成立。即函數連續不一定可導。
Th3: f ′ ( x 0 ) {f}'({{x}_{0}}) f ′ ( x 0 ) 存在⇔ f ′ − ( x 0 ) = f ′ + ( x 0 ) \Leftrightarrow {{{f}'}_{-}}({{x}_{0}})={{{f}'}_{+}}({{x}_{0}}) ⇔ f ′ − ( x 0 ) = f ′ + ( x 0 )
4.平面曲線的切線和法線
切線方程 : y − y 0 = f ′ ( x 0 ) ( x − x 0 ) y-{{y}_{0}}=f'({{x}_{0}})(x-{{x}_{0}}) y − y 0 = f ′ ( x 0 ) ( x − x 0 )
法線方程:y − y 0 = − 1 f ′ ( x 0 ) ( x − x 0 ) , f ′ ( x 0 ) ≠ 0 y-{{y}_{0}}=-\frac{1}{f'({{x}_{0}})}(x-{{x}_{0}}),f'({{x}_{0}})\ne 0 y − y 0 = − f ′ ( x 0 ) 1 ( x − x 0 ) , f ′ ( x 0 ) = 0
5.四則運算法則
設函數u = u ( x ) , v = v ( x ) u=u(x),v=v(x) u = u ( x ) , v = v ( x ) ]在點x x x 可導則
(1) ( u ± v ) ′ = u ′ ± v ′ (u\pm v{)}'={u}'\pm {v}' ( u ± v ) ′ = u ′ ± v ′ d ( u ± v ) = d u ± d v d(u\pm v)=du\pm dv d ( u ± v ) = d u ± d v
(2)( u v ) ′ = u v ′ + v u ′ (uv{)}'=u{v}'+v{u}' ( u v ) ′ = u v ′ + v u ′ d ( u v ) = u d v + v d u d(uv)=udv+vdu d ( u v ) = u d v + v d u
(3) ( u v ) ′ = v u ′ − u v ′ v 2 ( v ≠ 0 ) (\frac{u}{v}{)}'=\frac{v{u}'-u{v}'}{{{v}^{2}}}(v\ne 0) ( v u ) ′ = v 2 v u ′ − u v ′ ( v = 0 ) d ( u v ) = v d u − u d v v 2 d(\frac{u}{v})=\frac{vdu-udv}{{{v}^{2}}} d ( v u ) = v 2 v d u − u d v
6.基本導數與微分表
(1) y = c y=c y = c (常數) y ′ = 0 {y}'=0 y ′ = 0 d y = 0 dy=0 d y = 0
(2) y = x α y={{x}^{\alpha }} y = x α (α \alpha α 爲實數) y ′ = α x α − 1 {y}'=\alpha {{x}^{\alpha -1}} y ′ = α x α − 1 d y = α x α − 1 d x dy=\alpha {{x}^{\alpha -1}}dx d y = α x α − 1 d x
(3) y = a x y={{a}^{x}} y = a x y ′ = a x ln a {y}'={{a}^{x}}\ln a y ′ = a x ln a d y = a x ln a d x dy={{a}^{x}}\ln adx d y = a x ln a d x
特例: ( e x ) ′ = e x ({{{e}}^{x}}{)}'={{{e}}^{x}} ( e x ) ′ = e x d ( e x ) = e x d x d({{{e}}^{x}})={{{e}}^{x}}dx d ( e x ) = e x d x
(4) y = log a x y={{\log }_{a}}x y = log a x y ′ = 1 x ln a {y}'=\frac{1}{x\ln a} y ′ = x ln a 1
d y = 1 x ln a d x dy=\frac{1}{x\ln a}dx d y = x ln a 1 d x
特例:y = ln x y=\ln x y = ln x ( ln x ) ′ = 1 x (\ln x{)}'=\frac{1}{x} ( ln x ) ′ = x 1 d ( ln x ) = 1 x d x d(\ln x)=\frac{1}{x}dx d ( ln x ) = x 1 d x
(5) y = sin x y=\sin x y = sin x
y ′ = cos x {y}'=\cos x y ′ = cos x d ( sin x ) = cos x d x d(\sin x)=\cos xdx d ( sin x ) = cos x d x
(6) y = cos x y=\cos x y = cos x
y ′ = − sin x {y}'=-\sin x y ′ = − sin x d ( cos x ) = − sin x d x d(\cos x)=-\sin xdx d ( cos x ) = − sin x d x
(7) y = tan x y=\tan x y = tan x
y ′ = 1 cos 2 x = sec 2 x {y}'=\frac{1}{{{\cos }^{2}}x}={{\sec }^{2}}x y ′ = cos 2 x 1 = sec 2 x d ( tan x ) = sec 2 x d x d(\tan x)={{\sec }^{2}}xdx d ( tan x ) = sec 2 x d x
(8) y = cot x y=\cot x y = cot x y ′ = − 1 sin 2 x = − csc 2 x {y}'=-\frac{1}{{{\sin }^{2}}x}=-{{\csc }^{2}}x y ′ = − sin 2 x 1 = − csc 2 x d ( cot x ) = − csc 2 x d x d(\cot x)=-{{\csc }^{2}}xdx d ( cot x ) = − csc 2 x d x
(9) y = sec x y=\sec x y = sec x y ′ = sec x tan x {y}'=\sec x\tan x y ′ = sec x tan x
d ( sec x ) = sec x tan x d x d(\sec x)=\sec x\tan xdx d ( sec x ) = sec x tan x d x
(10) y = csc x y=\csc x y = csc x y ′ = − csc x cot x {y}'=-\csc x\cot x y ′ = − csc x cot x
d ( csc x ) = − csc x cot x d x d(\csc x)=-\csc x\cot xdx d ( csc x ) = − csc x cot x d x
(11) y = arcsin x y=\arcsin x y = arcsin x
y ′ = 1 1 − x 2 {y}'=\frac{1}{\sqrt{1-{{x}^{2}}}} y ′ = 1 − x 2 1
d ( arcsin x ) = 1 1 − x 2 d x d(\arcsin x)=\frac{1}{\sqrt{1-{{x}^{2}}}}dx d ( arcsin x ) = 1 − x 2 1 d x
(12) y = arccos x y=\arccos x y = arccos x
y ′ = − 1 1 − x 2 {y}'=-\frac{1}{\sqrt{1-{{x}^{2}}}} y ′ = − 1 − x 2 1 d ( arccos x ) = − 1 1 − x 2 d x d(\arccos x)=-\frac{1}{\sqrt{1-{{x}^{2}}}}dx d ( arccos x ) = − 1 − x 2 1 d x
(13) y = arctan x y=\arctan x y = arctan x
y ′ = 1 1 + x 2 {y}'=\frac{1}{1+{{x}^{2}}} y ′ = 1 + x 2 1 d ( arctan x ) = 1 1 + x 2 d x d(\arctan x)=\frac{1}{1+{{x}^{2}}}dx d ( arctan x ) = 1 + x 2 1 d x
(14) y = arc cot x y=\operatorname{arc}\cot x y = a r c cot x
y ′ = − 1 1 + x 2 {y}'=-\frac{1}{1+{{x}^{2}}} y ′ = − 1 + x 2 1
d ( arc cot x ) = − 1 1 + x 2 d x d(\operatorname{arc}\cot x)=-\frac{1}{1+{{x}^{2}}}dx d ( a r c cot x ) = − 1 + x 2 1 d x
(15) y = s h x y=shx y = s h x
y ′ = c h x {y}'=chx y ′ = c h x d ( s h x ) = c h x d x d(shx)=chxdx d ( s h x ) = c h x d x
(16) y = c h x y=chx y = c h x
y ′ = s h x {y}'=shx y ′ = s h x d ( c h x ) = s h x d x d(chx)=shxdx d ( c h x ) = s h x d x
7.複合函數,反函數,隱函數以及參數方程所確定的函數的微分法
(1) 反函數的運算法則: 設y = f ( x ) y=f(x) y = f ( x ) 在點x x x 的某鄰域內單調連續,在點x x x 處可導且f ′ ( x ) ≠ 0 {f}'(x)\ne 0 f ′ ( x ) = 0 ,則其反函數在點x x x 所對應的y y y 處可導,並且有d y d x = 1 d x d y \frac{dy}{dx}=\frac{1}{\frac{dx}{dy}} d x d y = d y d x 1
(2) 複合函數的運算法則:若 μ = φ ( x ) \mu =\varphi(x) μ = φ ( x ) 在點x x x 可導,而y = f ( μ ) y=f(\mu) y = f ( μ ) 在對應點μ \mu μ (μ = φ ( x ) \mu =\varphi (x) μ = φ ( x ) )可導,則複合函數y = f ( φ ( x ) ) y=f(\varphi (x)) y = f ( φ ( x ) ) 在點x x x 可導,且y ′ = f ′ ( μ ) ⋅ φ ′ ( x ) {y}'={f}'(\mu )\cdot {\varphi }'(x) y ′ = f ′ ( μ ) ⋅ φ ′ ( x )
(3) 隱函數導數d y d x \frac{dy}{dx} d x d y 的求法一般有三種方法:
1)方程兩邊對x x x 求導,要記住y y y 是x x x 的函數,則y y y 的函數是x x x 的複合函數.例如1 y \frac{1}{y} y 1 ,y 2 {{y}^{2}} y 2 ,l n y ln y l n y ,e y {{{e}}^{y}} e y 等均是x x x 的複合函數.
對x x x 求導應按複合函數連鎖法則做.
2)公式法.由F ( x , y ) = 0 F(x,y)=0 F ( x , y ) = 0 知 d y d x = − F ′ x ( x , y ) F ′ y ( x , y ) \frac{dy}{dx}=-\frac{{{{{F}'}}_{x}}(x,y)}{{{{{F}'}}_{y}}(x,y)} d x d y = − F ′ y ( x , y ) F ′ x ( x , y ) ,其中,F ′ x ( x , y ) {{{F}'}_{x}}(x,y) F ′ x ( x , y ) ,
F ′ y ( x , y ) {{{F}'}_{y}}(x,y) F ′ y ( x , y ) 分別表示F ( x , y ) F(x,y) F ( x , y ) 對x x x 和y y y 的偏導數
3)利用微分形式不變性
8.常用高階導數公式
(1)( a x ) ( n ) = a x ln n a ( a > 0 ) ( e x ) ( n ) = e x ({{a}^{x}}){{\,}^{(n)}}={{a}^{x}}{{\ln }^{n}}a\quad (a>{0})\quad \quad ({{{e}}^{x}}){{\,}^{(n)}}={e}{{\,}^{x}} ( a x ) ( n ) = a x ln n a ( a > 0 ) ( e x ) ( n ) = e x
(2)( sin k x ) ( n ) = k n sin ( k x + n ⋅ π 2 ) (\sin kx{)}{{\,}^{(n)}}={{k}^{n}}\sin (kx+n\cdot \frac{\pi }{{2}}) ( sin k x ) ( n ) = k n sin ( k x + n ⋅ 2 π )
(3)( cos k x ) ( n ) = k n cos ( k x + n ⋅ π 2 ) (\cos kx{)}{{\,}^{(n)}}={{k}^{n}}\cos (kx+n\cdot \frac{\pi }{{2}}) ( cos k x ) ( n ) = k n cos ( k x + n ⋅ 2 π )
(4)( x m ) ( n ) = m ( m − 1 ) ⋯ ( m − n + 1 ) x m − n ({{x}^{m}}){{\,}^{(n)}}=m(m-1)\cdots (m-n+1){{x}^{m-n}} ( x m ) ( n ) = m ( m − 1 ) ⋯ ( m − n + 1 ) x m − n
(5)( ln x ) ( n ) = ( − 1 ) ( n − 1 ) ( n − 1 ) ! x n (\ln x){{\,}^{(n)}}={{(-{1})}^{(n-{1})}}\frac{(n-{1})!}{{{x}^{n}}} ( ln x ) ( n ) = ( − 1 ) ( n − 1 ) x n ( n − 1 ) !
(6)萊布尼茲公式:若u ( x ) , v ( x ) u(x)\,,v(x) u ( x ) , v ( x ) 均n n n 階可導,則
( u v ) ( n ) = ∑ i = 0 n c n i u ( i ) v ( n − i ) {{(uv)}^{(n)}}=\sum\limits_{i={0}}^{n}{c_{n}^{i}{{u}^{(i)}}{{v}^{(n-i)}}} ( u v ) ( n ) = i = 0 ∑ n c n i u ( i ) v ( n − i ) ,其中u ( 0 ) = u {{u}^{({0})}}=u u ( 0 ) = u ,v ( 0 ) = v {{v}^{({0})}}=v v ( 0 ) = v
9.微分中值定理,泰勒公式
Th1: (費馬定理)
若函數f ( x ) f(x) f ( x ) 滿足條件:
(1)函數f ( x ) f(x) f ( x ) 在x 0 {{x}_{0}} x 0 的某鄰域內有定義,並且在此鄰域內恆有
f ( x ) ≤ f ( x 0 ) f(x)\le f({{x}_{0}}) f ( x ) ≤ f ( x 0 ) 或f ( x ) ≥ f ( x 0 ) f(x)\ge f({{x}_{0}}) f ( x ) ≥ f ( x 0 ) ,
(2) f ( x ) f(x) f ( x ) 在x 0 {{x}_{0}} x 0 處可導,則有 f ′ ( x 0 ) = 0 {f}'({{x}_{0}})=0 f ′ ( x 0 ) = 0
Th2: (羅爾定理)
設函數f ( x ) f(x) f ( x ) 滿足條件:
(1)在閉區間[ a , b ] [a,b] [ a , b ] 上連續;
(2)在( a , b ) (a,b) ( a , b ) 內可導;
(3)f ( a ) = f ( b ) f(a)=f(b) f ( a ) = f ( b ) ;
則在( a , b ) (a,b) ( a , b ) 內一存在個$\xi $,使 f ′ ( ξ ) = 0 {f}'(\xi )=0 f ′ ( ξ ) = 0
Th3: (拉格朗日中值定理)
設函數f ( x ) f(x) f ( x ) 滿足條件:
(1)在[ a , b ] [a,b] [ a , b ] 上連續;
(2)在( a , b ) (a,b) ( a , b ) 內可導;
則在( a , b ) (a,b) ( a , b ) 內一存在個$\xi $,使 f ( b ) − f ( a ) b − a = f ′ ( ξ ) \frac{f(b)-f(a)}{b-a}={f}'(\xi ) b − a f ( b ) − f ( a ) = f ′ ( ξ )
Th4: (柯西中值定理)
設函數f ( x ) f(x) f ( x ) ,g ( x ) g(x) g ( x ) 滿足條件:
(1) 在[ a , b ] [a,b] [ a , b ] 上連續;
(2) 在( a , b ) (a,b) ( a , b ) 內可導且f ′ ( x ) {f}'(x) f ′ ( x ) ,g ′ ( x ) {g}'(x) g ′ ( x ) 均存在,且g ′ ( x ) ≠ 0 {g}'(x)\ne 0 g ′ ( x ) = 0
則在( a , b ) (a,b) ( a , b ) 內存在一個$\xi $,使 f ( b ) − f ( a ) g ( b ) − g ( a ) = f ′ ( ξ ) g ′ ( ξ ) \frac{f(b)-f(a)}{g(b)-g(a)}=\frac{{f}'(\xi )}{{g}'(\xi )} g ( b ) − g ( a ) f ( b ) − f ( a ) = g ′ ( ξ ) f ′ ( ξ )
10.洛必達法則
法則Ⅰ (0 0 \frac{0}{0} 0 0 型)
設函數f ( x ) , g ( x ) f\left( x \right),g\left( x \right) f ( x ) , g ( x ) 滿足條件:
lim x → x 0 f ( x ) = 0 , lim x → x 0 g ( x ) = 0 \underset{x\to {{x}_{0}}}{\mathop{\lim }}\,f\left( x \right)=0,\underset{x\to {{x}_{0}}}{\mathop{\lim }}\,g\left( x \right)=0 x → x 0 lim f ( x ) = 0 , x → x 0 lim g ( x ) = 0 ;
f ( x ) , g ( x ) f\left( x \right),g\left( x \right) f ( x ) , g ( x ) 在x 0 {{x}_{0}} x 0 的鄰域內可導,(在x 0 {{x}_{0}} x 0 處可除外)且g ′ ( x ) ≠ 0 {g}'\left( x \right)\ne 0 g ′ ( x ) = 0 ;
lim x → x 0 f ′ ( x ) g ′ ( x ) \underset{x\to {{x}_{0}}}{\mathop{\lim }}\,\frac{{f}'\left( x \right)}{{g}'\left( x \right)} x → x 0 lim g ′ ( x ) f ′ ( x ) 存在(或$\infty $)。
則:
lim x → x 0 f ( x ) g ( x ) = lim x → x 0 f ′ ( x ) g ′ ( x ) \underset{x\to {{x}_{0}}}{\mathop{\lim }}\,\frac{f\left( x \right)}{g\left( x \right)}=\underset{x\to {{x}_{0}}}{\mathop{\lim }}\,\frac{{f}'\left( x \right)}{{g}'\left( x \right)} x → x 0 lim g ( x ) f ( x ) = x → x 0 lim g ′ ( x ) f ′ ( x ) 。
法則I ′ {{I}'} I ′ (0 0 \frac{0}{0} 0 0 型)設函數f ( x ) , g ( x ) f\left( x \right),g\left( x \right) f ( x ) , g ( x ) 滿足條件:
lim x → ∞ f ( x ) = 0 , lim x → ∞ g ( x ) = 0 \underset{x\to \infty }{\mathop{\lim }}\,f\left( x \right)=0,\underset{x\to \infty }{\mathop{\lim }}\,g\left( x \right)=0 x → ∞ lim f ( x ) = 0 , x → ∞ lim g ( x ) = 0 ;
存在一個X > 0 X>0 X > 0 ,當∣ x ∣ > X \left| x \right|>X ∣ x ∣ > X 時,f ( x ) , g ( x ) f\left( x \right),g\left( x \right) f ( x ) , g ( x ) 可導,且g ′ ( x ) ≠ 0 {g}'\left( x \right)\ne 0 g ′ ( x ) = 0 ;lim x → x 0 f ′ ( x ) g ′ ( x ) \underset{x\to {{x}_{0}}}{\mathop{\lim }}\,\frac{{f}'\left( x \right)}{{g}'\left( x \right)} x → x 0 lim g ′ ( x ) f ′ ( x ) 存在(或$\infty $)。
則lim x → x 0 f ( x ) g ( x ) = lim x → x 0 f ′ ( x ) g ′ ( x ) \underset{x\to {{x}_{0}}}{\mathop{\lim }}\,\frac{f\left( x \right)}{g\left( x \right)}=\underset{x\to {{x}_{0}}}{\mathop{\lim }}\,\frac{{f}'\left( x \right)}{{g}'\left( x \right)} x → x 0 lim g ( x ) f ( x ) = x → x 0 lim g ′ ( x ) f ′ ( x )
法則Ⅱ( ∞ ∞ \frac{\infty }{\infty } ∞ ∞ 型) 設函數 f ( x ) , g ( x ) f\left( x \right),g\left( x \right) f ( x ) , g ( x ) 滿足條件:
lim x → x 0 f ( x ) = ∞ , lim x → x 0 g ( x ) = ∞ \underset{x\to {{x}_{0}}}{\mathop{\lim }}\,f\left( x \right)=\infty,\underset{x\to {{x}_{0}}}{\mathop{\lim }}\,g\left( x \right)=\infty x → x 0 lim f ( x ) = ∞ , x → x 0 lim g ( x ) = ∞ ;
f ( x ) , g ( x ) f\left( x \right),g\left( x \right) f ( x ) , g ( x ) 在 x 0 {{x}_{0}} x 0 的鄰域內可導(在x 0 {{x}_{0}} x 0 處可除外)且g ′ ( x ) ≠ 0 {g}'\left( x \right)\ne 0 g ′ ( x ) = 0 ;lim x → x 0 f ′ ( x ) g ′ ( x ) \underset{x\to {{x}_{0}}}{\mathop{\lim }}\,\frac{{f}'\left( x \right)}{{g}'\left( x \right)} x → x 0 lim g ′ ( x ) f ′ ( x ) 存在(或$\infty ) 。 則 )。
則 ) 。 則 lim x → x 0 f ( x ) g ( x ) = lim x → x 0 f ′ ( x ) g ′ ( x ) \underset{x\to {{x}_{0}}}{\mathop{\lim }}\,\frac{f\left( x \right)}{g\left( x \right)}=\underset{x\to {{x}_{0}}}{\mathop{\lim }}\,\frac{{f}'\left( x \right)}{{g}'\left( x \right)} x → x 0 lim g ( x ) f ( x ) = x → x 0 lim g ′ ( x ) f ′ ( x ) $ 同理法則I I ′ {I{I}'} I I ′ ( ∞ ∞ \frac{\infty }{\infty } ∞ ∞ 型)仿法則 I ′ {{I}'} I ′ 可寫出。
11.泰勒公式
設函數f ( x ) f(x) f ( x ) 在點x 0 {{x}_{0}} x 0 處的某鄰域內具有n + 1 n+1 n + 1 階導數,則對該鄰域內異於x 0 {{x}_{0}} x 0 的任意點x x x ,在x 0 {{x}_{0}} x 0 與x x x 之間至少存在
一個ξ \xi ξ ,使得:
f ( x ) = f ( x 0 ) + f ′ ( x 0 ) ( x − x 0 ) + 1 2 ! f ′ ′ ( x 0 ) ( x − x 0 ) 2 + ⋯ f(x)=f({{x}_{0}})+{f}'({{x}_{0}})(x-{{x}_{0}})+\frac{1}{2!}{f}''({{x}_{0}}){{(x-{{x}_{0}})}^{2}}+\cdots f ( x ) = f ( x 0 ) + f ′ ( x 0 ) ( x − x 0 ) + 2 ! 1 f ′ ′ ( x 0 ) ( x − x 0 ) 2 + ⋯
+ f ( n ) ( x 0 ) n ! ( x − x 0 ) n + R n ( x ) +\frac{{{f}^{(n)}}({{x}_{0}})}{n!}{{(x-{{x}_{0}})}^{n}}+{{R}_{n}}(x) + n ! f ( n ) ( x 0 ) ( x − x 0 ) n + R n ( x )
其中 R n ( x ) = f ( n + 1 ) ( ξ ) ( n + 1 ) ! ( x − x 0 ) n + 1 {{R}_{n}}(x)=\frac{{{f}^{(n+1)}}(\xi )}{(n+1)!}{{(x-{{x}_{0}})}^{n+1}} R n ( x ) = ( n + 1 ) ! f ( n + 1 ) ( ξ ) ( x − x 0 ) n + 1 稱爲f ( x ) f(x) f ( x ) 在點x 0 {{x}_{0}} x 0 處的n n n 階泰勒餘項。
令x 0 = 0 {{x}_{0}}=0 x 0 = 0 ,則n n n 階泰勒公式
f ( x ) = f ( 0 ) + f ′ ( 0 ) x + 1 2 ! f ′ ′ ( 0 ) x 2 + ⋯ + f ( n ) ( 0 ) n ! x n + R n ( x ) f(x)=f(0)+{f}'(0)x+\frac{1}{2!}{f}''(0){{x}^{2}}+\cdots +\frac{{{f}^{(n)}}(0)}{n!}{{x}^{n}}+{{R}_{n}}(x) f ( x ) = f ( 0 ) + f ′ ( 0 ) x + 2 ! 1 f ′ ′ ( 0 ) x 2 + ⋯ + n ! f ( n ) ( 0 ) x n + R n ( x ) ……(1)
其中 R n ( x ) = f ( n + 1 ) ( ξ ) ( n + 1 ) ! x n + 1 {{R}_{n}}(x)=\frac{{{f}^{(n+1)}}(\xi )}{(n+1)!}{{x}^{n+1}} R n ( x ) = ( n + 1 ) ! f ( n + 1 ) ( ξ ) x n + 1 ,$\xi 在 0 與 在0與 在 0 與 x$之間.(1)式稱爲麥克勞林公式
常用五種函數在x 0 = 0 {{x}_{0}}=0 x 0 = 0 處的泰勒公式
(1) e x = 1 + x + 1 2 ! x 2 + ⋯ + 1 n ! x n + x n + 1 ( n + 1 ) ! e ξ {{{e}}^{x}}=1+x+\frac{1}{2!}{{x}^{2}}+\cdots +\frac{1}{n!}{{x}^{n}}+\frac{{{x}^{n+1}}}{(n+1)!}{{e}^{\xi }} e x = 1 + x + 2 ! 1 x 2 + ⋯ + n ! 1 x n + ( n + 1 ) ! x n + 1 e ξ
或 = 1 + x + 1 2 ! x 2 + ⋯ + 1 n ! x n + o ( x n ) =1+x+\frac{1}{2!}{{x}^{2}}+\cdots +\frac{1}{n!}{{x}^{n}}+o({{x}^{n}}) = 1 + x + 2 ! 1 x 2 + ⋯ + n ! 1 x n + o ( x n )
(2) sin x = x − 1 3 ! x 3 + ⋯ + x n n ! sin n π 2 + x n + 1 ( n + 1 ) ! sin ( ξ + n + 1 2 π ) \sin x=x-\frac{1}{3!}{{x}^{3}}+\cdots +\frac{{{x}^{n}}}{n!}\sin \frac{n\pi }{2}+\frac{{{x}^{n+1}}}{(n+1)!}\sin (\xi +\frac{n+1}{2}\pi ) sin x = x − 3 ! 1 x 3 + ⋯ + n ! x n sin 2 n π + ( n + 1 ) ! x n + 1 sin ( ξ + 2 n + 1 π )
或 = x − 1 3 ! x 3 + ⋯ + x n n ! sin n π 2 + o ( x n ) =x-\frac{1}{3!}{{x}^{3}}+\cdots +\frac{{{x}^{n}}}{n!}\sin \frac{n\pi }{2}+o({{x}^{n}}) = x − 3 ! 1 x 3 + ⋯ + n ! x n sin 2 n π + o ( x n )
(3) cos x = 1 − 1 2 ! x 2 + ⋯ + x n n ! cos n π 2 + x n + 1 ( n + 1 ) ! cos ( ξ + n + 1 2 π ) \cos x=1-\frac{1}{2!}{{x}^{2}}+\cdots +\frac{{{x}^{n}}}{n!}\cos \frac{n\pi }{2}+\frac{{{x}^{n+1}}}{(n+1)!}\cos (\xi +\frac{n+1}{2}\pi ) cos x = 1 − 2 ! 1 x 2 + ⋯ + n ! x n cos 2 n π + ( n + 1 ) ! x n + 1 cos ( ξ + 2 n + 1 π )
或 = 1 − 1 2 ! x 2 + ⋯ + x n n ! cos n π 2 + o ( x n ) =1-\frac{1}{2!}{{x}^{2}}+\cdots +\frac{{{x}^{n}}}{n!}\cos \frac{n\pi }{2}+o({{x}^{n}}) = 1 − 2 ! 1 x 2 + ⋯ + n ! x n cos 2 n π + o ( x n )
(4) ln ( 1 + x ) = x − 1 2 x 2 + 1 3 x 3 − ⋯ + ( − 1 ) n − 1 x n n + ( − 1 ) n x n + 1 ( n + 1 ) ( 1 + ξ ) n + 1 \ln (1+x)=x-\frac{1}{2}{{x}^{2}}+\frac{1}{3}{{x}^{3}}-\cdots +{{(-1)}^{n-1}}\frac{{{x}^{n}}}{n}+\frac{{{(-1)}^{n}}{{x}^{n+1}}}{(n+1){{(1+\xi )}^{n+1}}} ln ( 1 + x ) = x − 2 1 x 2 + 3 1 x 3 − ⋯ + ( − 1 ) n − 1 n x n + ( n + 1 ) ( 1 + ξ ) n + 1 ( − 1 ) n x n + 1
或 = x − 1 2 x 2 + 1 3 x 3 − ⋯ + ( − 1 ) n − 1 x n n + o ( x n ) =x-\frac{1}{2}{{x}^{2}}+\frac{1}{3}{{x}^{3}}-\cdots +{{(-1)}^{n-1}}\frac{{{x}^{n}}}{n}+o({{x}^{n}}) = x − 2 1 x 2 + 3 1 x 3 − ⋯ + ( − 1 ) n − 1 n x n + o ( x n )
(5) ( 1 + x ) m = 1 + m x + m ( m − 1 ) 2 ! x 2 + ⋯ + m ( m − 1 ) ⋯ ( m − n + 1 ) n ! x n {{(1+x)}^{m}}=1+mx+\frac{m(m-1)}{2!}{{x}^{2}}+\cdots +\frac{m(m-1)\cdots (m-n+1)}{n!}{{x}^{n}} ( 1 + x ) m = 1 + m x + 2 ! m ( m − 1 ) x 2 + ⋯ + n ! m ( m − 1 ) ⋯ ( m − n + 1 ) x n
+ m ( m − 1 ) ⋯ ( m − n + 1 ) ( n + 1 ) ! x n + 1 ( 1 + ξ ) m − n − 1 +\frac{m(m-1)\cdots (m-n+1)}{(n+1)!}{{x}^{n+1}}{{(1+\xi )}^{m-n-1}} + ( n + 1 ) ! m ( m − 1 ) ⋯ ( m − n + 1 ) x n + 1 ( 1 + ξ ) m − n − 1
或( 1 + x ) m = 1 + m x + m ( m − 1 ) 2 ! x 2 + ⋯ {{(1+x)}^{m}}=1+mx+\frac{m(m-1)}{2!}{{x}^{2}}+\cdots ( 1 + x ) m = 1 + m x + 2 ! m ( m − 1 ) x 2 + ⋯ ,+ m ( m − 1 ) ⋯ ( m − n + 1 ) n ! x n + o ( x n ) +\frac{m(m-1)\cdots (m-n+1)}{n!}{{x}^{n}}+o({{x}^{n}}) + n ! m ( m − 1 ) ⋯ ( m − n + 1 ) x n + o ( x n )
12.函數單調性的判斷
Th1: 設函數f ( x ) f(x) f ( x ) 在( a , b ) (a,b) ( a , b ) 區間內可導,如果對∀ x ∈ ( a , b ) \forall x\in (a,b) ∀ x ∈ ( a , b ) ,都有f ′ ( x ) > 0 f\,'(x)>0 f ′ ( x ) > 0 (或f ′ ( x ) < 0 f\,'(x)<0 f ′ ( x ) < 0 ),則函數f ( x ) f(x) f ( x ) 在( a , b ) (a,b) ( a , b ) 內是單調增加的(或單調減少)
Th2: (取極值的必要條件)設函數f ( x ) f(x) f ( x ) 在x 0 {{x}_{0}} x 0 處可導,且在x 0 {{x}_{0}} x 0 處取極值,則f ′ ( x 0 ) = 0 f\,'({{x}_{0}})=0 f ′ ( x 0 ) = 0 。
Th3: (取極值的第一充分條件)設函數f ( x ) f(x) f ( x ) 在x 0 {{x}_{0}} x 0 的某一鄰域內可微,且f ′ ( x 0 ) = 0 f\,'({{x}_{0}})=0 f ′ ( x 0 ) = 0 (或f ( x ) f(x) f ( x ) 在x 0 {{x}_{0}} x 0 處連續,但f ′ ( x 0 ) f\,'({{x}_{0}}) f ′ ( x 0 ) 不存在。)
(1)若當x x x 經過x 0 {{x}_{0}} x 0 時,f ′ ( x ) f\,'(x) f ′ ( x ) 由“+”變“-”,則f ( x 0 ) f({{x}_{0}}) f ( x 0 ) 爲極大值;
(2)若當x x x 經過x 0 {{x}_{0}} x 0 時,f ′ ( x ) f\,'(x) f ′ ( x ) 由“-”變“+”,則f ( x 0 ) f({{x}_{0}}) f ( x 0 ) 爲極小值;
(3)若f ′ ( x ) f\,'(x) f ′ ( x ) 經過x = x 0 x={{x}_{0}} x = x 0 的兩側不變號,則f ( x 0 ) f({{x}_{0}}) f ( x 0 ) 不是極值。
Th4: (取極值的第二充分條件)設f ( x ) f(x) f ( x ) 在點x 0 {{x}_{0}} x 0 處有f ′ ′ ( x ) ≠ 0 f''(x)\ne 0 f ′ ′ ( x ) = 0 ,且f ′ ( x 0 ) = 0 f\,'({{x}_{0}})=0 f ′ ( x 0 ) = 0 ,則 當f ′ ′ ( x 0 ) < 0 f'\,'({{x}_{0}})<0 f ′ ′ ( x 0 ) < 0 時,f ( x 0 ) f({{x}_{0}}) f ( x 0 ) 爲極大值;
當f ′ ′ ( x 0 ) > 0 f'\,'({{x}_{0}})>0 f ′ ′ ( x 0 ) > 0 時,f ( x 0 ) f({{x}_{0}}) f ( x 0 ) 爲極小值。
注:如果f ′ ′ ( x 0 ) < 0 f'\,'({{x}_{0}})<0 f ′ ′ ( x 0 ) < 0 ,此方法失效。
13.漸近線的求法
(1)水平漸近線 若lim x → + ∞ f ( x ) = b \underset{x\to +\infty }{\mathop{\lim }}\,f(x)=b x → + ∞ lim f ( x ) = b ,或lim x → − ∞ f ( x ) = b \underset{x\to -\infty }{\mathop{\lim }}\,f(x)=b x → − ∞ lim f ( x ) = b ,則
y = b y=b y = b 稱爲函數y = f ( x ) y=f(x) y = f ( x ) 的水平漸近線。
(2)鉛直漸近線 若lim x → x 0 − f ( x ) = ∞ \underset{x\to x_{0}^{-}}{\mathop{\lim }}\,f(x)=\infty x → x 0 − lim f ( x ) = ∞ ,或lim x → x 0 + f ( x ) = ∞ \underset{x\to x_{0}^{+}}{\mathop{\lim }}\,f(x)=\infty x → x 0 + lim f ( x ) = ∞ ,則
x = x 0 x={{x}_{0}} x = x 0 稱爲y = f ( x ) y=f(x) y = f ( x ) 的鉛直漸近線。
(3)斜漸近線 若a = lim x → ∞ f ( x ) x , b = lim x → ∞ [ f ( x ) − a x ] a=\underset{x\to \infty }{\mathop{\lim }}\,\frac{f(x)}{x},\quad b=\underset{x\to \infty }{\mathop{\lim }}\,[f(x)-ax] a = x → ∞ lim x f ( x ) , b = x → ∞ lim [ f ( x ) − a x ] ,則
y = a x + b y=ax+b y = a x + b 稱爲y = f ( x ) y=f(x) y = f ( x ) 的斜漸近線。
14.函數凹凸性的判斷
Th1: (凹凸性的判別定理)若在I上f ′ ′ ( x ) < 0 f''(x)<0 f ′ ′ ( x ) < 0 (或f ′ ′ ( x ) > 0 f''(x)>0 f ′ ′ ( x ) > 0 ),則f ( x ) f(x) f ( x ) 在I上是凸的(或凹的)。
Th2: (拐點的判別定理1)若在x 0 {{x}_{0}} x 0 處f ′ ′ ( x ) = 0 f''(x)=0 f ′ ′ ( x ) = 0 ,(或f ′ ′ ( x ) f''(x) f ′ ′ ( x ) 不存在),當x x x 變動經過x 0 {{x}_{0}} x 0 時,f ′ ′ ( x ) f''(x) f ′ ′ ( x ) 變號,則( x 0 , f ( x 0 ) ) ({{x}_{0}},f({{x}_{0}})) ( x 0 , f ( x 0 ) ) 爲拐點。
Th3: (拐點的判別定理2)設f ( x ) f(x) f ( x ) 在x 0 {{x}_{0}} x 0 點的某鄰域內有三階導數,且f ′ ′ ( x ) = 0 f''(x)=0 f ′ ′ ( x ) = 0 ,f ′ ′ ′ ( x ) ≠ 0 f'''(x)\ne 0 f ′ ′ ′ ( x ) = 0 ,則( x 0 , f ( x 0 ) ) ({{x}_{0}},f({{x}_{0}})) ( x 0 , f ( x 0 ) ) 爲拐點。
15.弧微分
d S = 1 + y ′ 2 d x dS=\sqrt{1+y{{'}^{2}}}dx d S = 1 + y ′ 2 d x
16.曲率
曲線y = f ( x ) y=f(x) y = f ( x ) 在點( x , y ) (x,y) ( x , y ) 處的曲率k = ∣ y ′ ′ ∣ ( 1 + y ′ 2 ) 3 2 k=\frac{\left| y'' \right|}{{{(1+y{{'}^{2}})}^{\tfrac{3}{2}}}} k = ( 1 + y ′ 2 ) 2 3 ∣ y ′ ′ ∣ 。
對於參數方程KaTeX parse error: No such environment: align at position 15: \left\{ \begin{̲a̲l̲i̲g̲n̲}̲ & x=\varphi (…
k = ∣ φ ′ ( t ) ψ ′ ′ ( t ) − φ ′ ′ ( t ) ψ ′ ( t ) ∣ [ φ ′ 2 ( t ) + ψ ′ 2 ( t ) ] 3 2 k=\frac{\left| \varphi '(t)\psi ''(t)-\varphi ''(t)\psi '(t) \right|}{{{[\varphi {{'}^{2}}(t)+\psi {{'}^{2}}(t)]}^{\tfrac{3}{2}}}} k = [ φ ′ 2 ( t ) + ψ ′ 2 ( t ) ] 2 3 ∣ φ ′ ( t ) ψ ′ ′ ( t ) − φ ′ ′ ( t ) ψ ′ ( t ) ∣ 。
17.曲率半徑
曲線在點M M M 處的曲率k ( k ≠ 0 ) k(k\ne 0) k ( k = 0 ) 與曲線在點M M M 處的曲率半徑ρ \rho ρ 有如下關係:ρ = 1 k \rho =\frac{1}{k} ρ = k 1 。
參考:https://aistudio.baidu.com/aistudio/projectdetail/549642