The Real And Complex Number Systems

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lim n→ inf a n . That is, lim n→ inf a n sup c n . n If every c n −, then we define lim n→ inf a n −. Remark The concept of lower limit and upper limit first appear in the book (Analyse Alge’brique) written by Cauchy in 1821. But until 1882, Paul du Bois-Reymond gave explanations on them, it becomes well-known. Example 1 −1 n n1 0,2,0,2,..., sowehave b n 2andc n 0 for all n which implies that lim sup a n 2 and lim inf a n 0. Example −1 n n n1 −1, 2, −3,4,..., sowehave b n and c n − for all n which implies that lim sup a n and lim inf a n −. −n n1 Example −1, −2, −3, . . . , sowehave b n −n and c n − for all n which implies that lim sup a n − and lim inf a n −. Relations with convergence and divergence for upper (lower) limit Theorem Let a n be a real sequence, then a n converges if, and only if, the upper limit and the lower limit are real with lim n→ sup a n lim n→ inf a n lim n→ a n . Theorem Let a n be a real sequence, then we have (1) lim n→ sup a n a n has no upper bound. (2) lim n→ sup a n − for any M 0, there is a positive integer n 0 such that as n ≥ n 0 ,wehave a n ≤−M. (3) lim n→ sup a n a if, and only if, (a) given any 0, there are infinite many numbers n such that a − a n and (b) given any 0, there is a positive integer n 0 such that as n ≥ n 0 ,wehave a n a . Similarly, we also have Theorem Let a n be a real sequence, then we have
(1) lim n→ inf a n − a n has no lower bound. (2) lim n→ inf a n for any M 0, there is a positive integer n 0 such that as n ≥ n 0 ,wehave a n ≥ M. (3) lim n→ inf a n a if, and only if, (a) given any 0, there are infinite many numbers n such that a a n and (b) given any 0, there is a positive integer n 0 such that as n ≥ n 0 ,wehave a n a − . From Theorem 2 an Theorem 3, the sequence is divergent, we give the following definitios. Definition Let a n be a real sequence, then we have (1) If lim n→ sup a n −, then we call the sequence a n diverges to −, denoted by lim n→ a n −. Theorem Theorem Theorem (2) If lim n→ inf a n , then we call the sequence a n diverges to , denoted by lim n→ a n . Let a n be a real sequence. If a is a limit point of a n , then we have lim n→ inf a n ≤ a ≤ lim n→ sup a n . Some useful results Let a n be a real sequence, then (1) lim n→ inf a n ≤ lim n→ sup a n . (2) lim n→ inf−a n − lim n→ sup a n and lim n→ sup−a n − lim n→ inf a n (3) If every a n 0, and 0 lim n→ inf a n ≤ lim n→ sup a n , then we have lim n→ sup a 1 n 1 lim n→ inf a n Let a n and b n be two real sequences. (1) If there is a positive integer n 0 such that a n ≤ b n , then we have lim n→ inf a n ≤ lim n→ inf b n and lim n→ sup a n ≤ lim n→ sup b n . (2) Suppose that − lim n→ inf a n , lim n→ inf b n , lim n→ sup a n , lim n→ sup b n , then lim n→ inf a n lim n→ inf b n and lim n→ inf 1 a n 1 lim n→ sup a n . ≤ lim n→ infa n b n ≤ lim n→ inf a n lim n→ sup b n (or lim n→ sup a n lim n→ inf b n ) ≤ lim n→ supa n b n ≤ lim n→ sup a n lim n→ sup b n .
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The Real And Complex Number Systems
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Proof: Consider 2n−2 ∑ (x + 1)
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Then S = N. Proof: (A ⇒ B): If S
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Note: There are many and many metho
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In addition, (√ a ) 2 − − b (
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Proof: Say {ar + b : a ∈ Z, b ∈
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(⇐)It is clear since every a n is
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Proof: Choose a 0 = [x], and thus c
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Proof: Use Cauchy-Schwarz inequalit
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In addition, ∑ a k b k + a j b j
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So, z 1 z 2 = ¯z 1¯z 2 (c) z¯z =
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so, |a − b| 2 ≤ ( 1 + |a| 2) (
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Proof: Note that in this text book,
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1.39 State and prove a theorem anal
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1.43 (a) Prove that Log (z w ) = wL
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For complex θ, we show that it hol
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So, ix−y = i (x + iy) = iz = log
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and the sum of their squares is giv
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Some Basic Notations Of Set Theory
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(i) If x ∈ R, it is clear that (x
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(a) A ∪ (B ∪ C) = (A ∪ B) ∪
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(e) A ∩ (B − C) = (A ∩ B) −
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Proof: Given x ∈ X, then f (x)
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By hyppothesis, we get T ⊆ f (S)
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Proof: Since S is an infinite set,
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Proof: Assume S˜R and let f be a o
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2.22 Let S denote the collection of
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Charpter 3 Elements of Point set To
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And thus by the remark in (e), it i
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3.7 Prove that a nonempty, bounded
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Bx, r x S Bx, r x T . So, at
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Claim that Bp, r S as follows. Let
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Covering theorems in R n 3.17 If S
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uncountable. Hence, by exercise 3.2
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Then we have (a) (b) (c) (d) x y
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(b) Give an example of a metric spa
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Hence from (1)-(4), we know that i
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3.44 intM A M A . Proof: Let B
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That is, intB which is absurb. He
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Limits And Continuity Limits of seq
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x n1 x n 1 1 x n x n 1 2 . Rema
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|a m a n| |a m a m1 a m1 a m2
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and use the fact if a n converges
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lim y0 fx, y 0ifx 0, 1ifx 0. and
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fx, y 1 r cos sinr2 cossin if x
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then we have lim fx, y L if x 0an
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this is because a can be an isolate
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irrational. Prove that: (a) ffx x
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In addition, since f1 f1 by f0 0,
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lim r n0 fx f lim n x n lim n fx
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if x Q, andgx 0ifx Q c . Remark:
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number f T supfx fy : x, y T is
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Proof: Since the hypothesis says th
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(f) S 0, 1 0, 1, T 0, 1 0, 1. S
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In Exercises 4.29 through 4.33, we
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function. Since f0, 1 0, 1 0, 1,
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4.40 If x is a point in a metric sp
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from b to A) are disjoint. So, if e
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x F k1 F k A B U V which im
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Proof: Assume that B C 1 is discon
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Proof: By Mean Value Theorem, wehav
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x r y r rz r1 x y ry r1 /2. So,
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hx gfx if x S. Iff is uniformly c
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dx, y , x, y A, wehave dfx, fy
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In addition, part (b) comes from in
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continuous at a, a. (2) (x y) Sinc
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Proof: Let D denote the set of dico
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(a) Provet that the formula df, g
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so, by induction, we find dp n1 , p
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Proof: If p and p are fixed points
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(b) Assume there is a subsequence p
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Hence, f is increasing on , a/3 a
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f k x f k 0 x 0 fk x x by induct
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h k1 h k k jk f j g kj x j0
Page 149 and 150: g x g x 3 2 a d f x a d f x 3 2
Page 151 and 152: which implies that F 0, where
Page 153 and 154: g fx gfx. Assume that there is a
Page 155 and 156: Remark: For x 0, we can show that
Page 157 and 158: Proof: Look at the Generalized Mean
Page 159 and 160: Proof: By Generalized Mean Value Th
Page 161 and 162: there is a point p such that fp 0.
Page 163 and 164: Remark: If we can make sure that fx
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Page 167 and 168: fx fy x y f x /2 *’ Combi
Page 169 and 170: lim xa fx gx L. Remark: 1. The pr
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Page 173 and 174: f x 1 ...x n n f x 1 ...x n1 n x
Page 175 and 176: f x 1 ...x n n fx 1 ...fx n n . C
Page 177 and 178: lx fc f cx c fx. (Exercise 2)
Page 179 and 180: So, we have Partial derivatives fb
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Page 183 and 184: ux, y (1) arctany/x, ifx 0, y R
Page 185 and 186: Functions of Bounded Variation and
Page 187 and 188: For the part fx x fy 1 |fx fy| 1
Page 189 and 190: Claim that 1 sup A. Suppose NOT, t
Page 191 and 192: we know that V f is an increasing
Page 193 and 194: in Section 6.12. Proof: Sinceft : t
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Page 197 and 198: n k1 n ||fb k | |fa k || |fb k
Page 199: Supplement on lim sup and lim inf I
Page 203 and 204: Remark: The exercise is useful in t
Page 205 and 206: which implies that c ≤ a b since
Page 207 and 208: If lim sup n→ a n1 a n , then it
Page 209 and 210: We first prove lim n→ sup n ≤
Page 211 and 212: 0 ≤ d 1 * by Theorem 8.23 (i). N
Page 213 and 214: Consider which implies that which i
Page 215 and 216: So, L 1 5 since L ≥ 1. 2 Remark:
Page 217 and 218: For case (i), since 1 n log nlog lo
Page 219 and 220: ()Assume that ∑ n1 That is, p!
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Page 223 and 224: (b) Prove that ∑ n1 −1 n−1 /
Page 225 and 226: then b k sin kx, a k1 − a k 1
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Page 229 and 230: Suppose NOT, it means that lim n→
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Page 233 and 234: |sin k|r ∑ k So, ∑ |sink|r dive
Page 235 and 236: n For the part 1 2 0 that x sint
Page 237 and 238: lim n→ sin ... sin n 1 ... 1 n
Page 239 and 240: Also, lim q→ fp, q lim q→ p si
Page 241 and 242: n c n ∑ a k b n−k k0 n ∑ k0
Page 243 and 244: So, n s n ∑ cos2k − 1x j1 sin
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Page 247 and 248: which implies that which implies th
Page 249 and 250: So, by above sayings, we have prove
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(a) If fn is multiplicative and if
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Sequences of Functions Uniform conv
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(b) Prove that h n (x) does not con
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Proof: Since g is continuous on a c
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Hence, {g (x) x n } converges unifo
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y continuity of f k(x0 ) (x) − f
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In addition, as c ≥ 1/2, if f n
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(Lemma) If {a n } and {b n } are tw
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9.16 Let {f n } be a sequence of re
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which implies that ∣ lim sup 1 k
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have ∫ x 0 ∞∑ t 2n − 1 2 n=
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[ ] π And as x ∈ , π , then n+p
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0.1 Supplement on some results on W
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which implies that h (x + t) − h
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we have ∫ d c |f n − g| 2 dx
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we complete it. 9.31 Given that two
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if x = λ (≠ 0) is a root of 1 +
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So, the series diverges. (ii) As
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9.38 For each real t, define f t (x
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So, B 0 = P 0 (0) = C 0 = 1, B 1 =
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Remark: (1) The reader can see the
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That is, lim n inf a n sup c n . n
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and lim n infa n b n lim n a n
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q! kq1 1 k! kq1 q! k! 1 q 1
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g x log 1 1 x x a x 2 x log
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The Real And Complex Number Systems

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