積分的一些問題(變數代換和均值定理)

2013-07-16 9:52 am
1. 去不定積分sinxcosx(sinx+1)root dx
也就去積分 sinx 乘上 cosx乘上根號sinx+1乘上dx

2.Let f(x) = x^3-x^2-x+1 on [-1,2]. Find all numbers c satisfying the conclusion to the Mean Value Theorem.

回答 (2)

2013-07-16 10:12 am
✔ 最佳答案
1.∫sin(x)cos(x)√(sin(x)+1) dx令 u = √(sin(x)+1)
則 sin(x) = u^2-1,
  cos(x) dx = 2u du
所以
  ∫sin(x)cos(x)√(sin(x)+1) dx
   = ∫(u^2-1)(u)(2u)du
   = ∫2(u^4-u^2) du
   = (2/5)u^5 - (2/3)u^3 + C
   = (2/5)(sin(x)+1)^{5/2}-(2/3)(sin(x)+1)^{3/2}+C
2. f(x) = x^3-x^2-x+1 on [-1,2]
均值定理說: 存在 c 在 -1 與 2 之間, 使
f'(c) = (f(2)-f(-1))/[2-(-1)]
   = [(8-4-2+1)-(-1-1+1+1)]/3
   = 1又: f'(x) = 3x^2-2x-1
所以 1 = 3c^2-2c-1
解之, 得 c = (-1±√7)/3.
c 介於 -1 與 2 之間, 故 c = (-1+√7)/3.


2013-07-16 10:36 am

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希望能幫助到你 :)

2013-07-16 02:41:55 補充:
圖片網址:
http://imgcld.yimg.com/8/n/HA00299181/o/20130716023323.jpg
參考: 我本人


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