[單變] 幾題,出在"極限與連續"章節中

看板trans_math作者 (mercedesff)時間15年前 (2010/12/04 21:59), 編輯推噓0(0010)
留言10則, 1人參與, 最新討論串1/1
以下想破頭,仍不得其解,請大大幫忙(跪),謝謝! ╭ 1, if x=1; 1. Let f(x) = ┤ ╰ 2, if x=2. Is f a continuous function on its domain? Justify your answer. 2. Suppose that f:[a,b]→R is a continuous function. (a) Let a ≦ x_1 < x_2 ≦ b . Prove that there is a point z 屬於 [a,b] such that f(x_1) + f(x_2) f(z) = 一一一一一一一一一一一 . 2 (b) Let a ≦ x_1 < x_2 < x_3 ≦ b . Prove that there is a point z 屬於 [a,b] such that f(x_1) + f(x_2) + f(x_3) f(z) = 一一一一一一一一一一一一一一一 . 3 3. Let f:(-∞,∞) → R be a continuous function such that there are two real numbers a and b, such that f(a) ≦ f(x) ≦f(b) for all -∞ < x < ∞ . Is the equation f(x) - x = 0 solvable ? ~~~~~ Justify your answer. -- ※ 發信站: 批踢踢實業坊(ptt.cc) ◆ From: 140.113.90.123

12/06 21:44, , 1F
2.Let F(x)=f(x)-0.5[f(x1)+f(x2)]
12/06 21:44, 1F

12/06 21:46, , 2F
設f(x1)>f(x2),再用中間值定理
12/06 21:46, 2F

12/06 21:47, , 3F
b部分就取max和min之後用中間值定理吧
12/06 21:47, 3F

12/06 21:48, , 4F
Let M=Max(f1,f2,f3),m=min(f1,f2,f3)
12/06 21:48, 4F

12/06 21:49, , 5F
Is the equation f(x)-x=0是在問什麼?
12/06 21:49, 5F
對不起,題目少打一個字,已改於上面了 ※ 編輯: mercedesff 來自: 140.113.90.123 (12/08 18:30)

12/09 23:40, , 6F
那就設F(x)=f(x)-x 利用f(x)的有界性
12/09 23:40, 6F

12/09 23:42, , 7F
F(x)→-∞ as x→∞
12/09 23:42, 7F

12/09 23:42, , 8F
F(x)→∞ as x→-∞
12/09 23:42, 8F

12/09 23:43, , 9F
由中值定理就可以了
12/09 23:43, 9F

12/09 23:44, , 10F
第一題定義域只有兩個點 我也看不懂
12/09 23:44, 10F
文章代碼(AID): #1C-aaaRU (trans_math)