【高等数学】微分学的应用

时间:2024-11-08 19:44:43

中值定理

罗尔中值定理

  • f f f [ a , b ] [a,b] [a,b] 区间上连续,
  • ( a , b ) (a,b) (a,b) 上可导,
  • f ( a ) = f ( b ) f(a)=f(b) f(a)=f(b)
  • 则存在 ξ ∈ [ a , b ] \xi\in [a,b] ξ[a,b], f ′ ( ξ ) = 0 f'(\xi)=0 f(ξ)=0

拉格朗日中值定理

  • f f f [ a , b ] [a,b] [a,b] 区间上连续,
  • ( a , b ) (a,b) (a,b) 上可导,
  • 则存在 ξ ∈ [ a , b ] \xi\in [a,b] ξ[a,b], f ′ ( ξ ) = f ( b ) − f ( a ) b − a f'(\xi)= \frac{f(b)-f(a)}{b-a} f(ξ)=baf(b)f(a)
  • 拉格朗日余项 ∃ ξ \exists \xi ξ, f ( b ) = f ( a ) + f ′ ( ξ ) ( b − a ) f(b)=f(a)+f'(\xi)(b-a) f(b)=f(a)+f(ξ)(ba)
  • 柯西余项 f ( b ) = f ( a ) + ( b − a ) ∫ 0 1 f ′ ( a + t ( b − a ) ) d t f(b)=f(a)+(b-a)\int_0^1 f'(a+t(b-a)) dt f(b)=f(a)+(ba)01f(a+t(ba))dt

柯西中值定理

  • f f f, g g g [ a , b ] [a,b] [a,b] 区间上连续,
  • ( a , b ) (a,b) (a,b) 上可导,
  • 则存在 ξ ∈ [ a , b ] \xi\in [a,b] ξ[a,b], f ′ ( ξ ) g ′ ( ξ ) = f ( b ) − f ( a ) g ( b ) − g ( a ) \frac{f'(\xi)}{g'(\xi)}= \frac{f(b)-f(a)}{g(b)-g(a)} g(ξ)f(ξ)=g(b)g(a)f(b)f(a)

泰勒中值定理

  • f f f x 0 x_0 x0 的某个邻域 U ( x 0 ) U(x_0) U(x0)上连续,
  • U ( x 0 ) U(x_0) U(x0) n n n 阶可导,
  • 则存在 θ ∈ [ 0 , 1 ] \theta\in [0,1] θ[0,1], z θ = x + θ ( y − x ) z_\theta=x+\theta(y-x) zθ=x+θ(yx),
    拉格朗日余项 f ( y ) = f ( x ) + f ′ ( x ) ( y − x ) + f ′ ′ ( x ) 2 ( y − x ) 2 + ⋯ + f ( n ) ( x ) n ! ( y − x ) n + f ( n + 1 ) ( z θ ) ( n + 1 ) ! ( y − x ) n + 1 f(y)= f(x) +f'(x)(y-x)+ \frac{f''(x)}{2}(y-x)^2+ \cdots+ \frac{f^{(n)}(x)}{n!}(y-x)^n +\frac{f^{(n+1)}(z_\theta)}{(n+1)!}(y-x)^{n+1} f(y)=f(x)+f(x)(yx)+2f′′(x)(yx)2++n!f(n)(x)(yx)n+(n+1)!f(n+1)(zθ)(yx)n+1
  • 柯西余项 f ( y ) = f ( x ) + f ′ ( x ) ( y − x ) + f ′ ′ ( x ) 2 ( y − x ) 2 + ⋯ + f ( n ) ( x ) n ! ( y − x ) n + ∫ 0 1 f ( n + 1 ) ( z θ ) d θ ( n + 1 ) ! ( y − x ) n + 1 f(y)= f(x) +f'(x)(y-x)+ \frac{f''(x)}{2}(y-x)^2+ \cdots+ \frac{f^{(n)}(x)}{n!}(y-x)^n+\frac{\int_0^1 f^{(n+1)}(z_\theta)d \theta}{(n+1)!} (y-x)^{n+1} f(y)=f(x)+f(x)(yx)+2f′′(x)(yx)2++n!f(n)(x)(yx)n+(n+1)!01