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48 Cards in this Set

  • Front
  • Back
Well-Ordering Principle of N
Every nonempty subset of N has a least element.
Algebraic properties of R
The order properties of R
There is a nonempty subset P of R, called the positive real numbers, with these properties:
(1)If a,b belong to P, then A+B belongs to P.
(2)If a,b belong to P, then ab belongs to P.
(3)Trichotomy Property
Trichotomy Property
If a belongs to R, then one of the following holds:
a∈P, a=0, -a∈P
The notion of inequality btw 2 real numbers
Let a,b be elements of R.
(a)If a-b∈P, then a>b or b<a
(b)If a-b∈P∐{0}, then a≥b or b≤a
4 Results of ordering properties of R
1)If a>b and b>c then a>c
2)If a>b then a+b>b+c
3)If a>b and c>0 then ca>cb.
4)If a>b and c<0 then ca<cb.
The absolute value of a real number a is
. a if a>0
. 0 is a=0
. -a if a<0
Triangle Inequality
If a,b∈R, then ∣a+b∣≤∣a∣+∣b∣
Two variations of the triangle inequality
. ∣∣a∣-∣b∣∣≤∣a-b∣
. ∣a-b∣≤∣a∣+∣b∣
Additional(4) Properties of absolute value
(a) ∣ab∣=∣a∣∣b∣ ∀ a,b∈R
(b) ∣a∣^2 = a^2 ∀ a∈R
(c) If c≥0, then ∣a∣≤c iff -c≤a≤c
(d) -∣a∣≤a≤∣a∣
Let a∈R and ε>0. Then the ε-neighborhood of a
is the set Vε(a):={x∈R:∣x-a∣<ε}
For a∈R, the statement that x belongs to Vε(a) is equivalent to
-ε<x-a<ε and a-ε<x<a+ε
Let a∈R. If x belongs to the neighborhood Vε(a) for every ε>0,
then x=a
Let S be a nonempty subset of R.
The set S is said to be bounded above if
∃ a number u∈R s.t. s≤u ∀s∈S.
u is called an upper bound of S.
Let S be a nonempty subset of R.
The set S is said to be bounded below if
∃ a number w∈R s.t. w≤s ∀s∈S.
w is called a lower bound of S.
Let S be a nonempty subset of R.
A set is said to be bounded if
it is both bounded above and bounded below.
Let S be a nonempty subset of R.
A set is said to be unbounded if
it is not bounded.
Let S be a nonempty subset of R.
If S is bounded above, then a number u is said to be a supremum (a least upper bound) of S if it
(1)u is an upper bound of S, and
(2)if v is any upper bound of S, then u≤v

sup S
Let S be a nonempty subset of R.
If S is bounded below, then a number w is said to be an infimum (a greatest lower bound) of S if it
(1)w is a lower bound of S, and
(2)if t is any lower bound of S, then t≤w

inf S
Archimedean Property
IF x∈R, then ∃ nₓ∈N s.t. x<nₓ
If a,b∈R satisfy a<b, then the open interval set is
If a,b∈R satisfy a≤b, then the closed interval set is
Characterization Theorem
If S is a subset of R that contains at least two points and has the property,
(1)if x,y∈S and x<y, then [x,y]⊆S, then S is an interval.
Nested Intervals
A sequence of intervals I(n), n∈N is nested if
Nested Intervals Property
If Iₓ=[aₓ,bₓ], x∈N is a nested sequence of closed bounded intervals, then ∃ a number έ∈R s.t έ∈Iₓ for all x∈N
A sequence of real numbers is a function
defined on the set N={1,2,...._ of natural numbers whose range is contained in the set R of real numbers.
Subsequence definition

Let X=x(n) be a sequence of real numbers and let n₁<n₂<....<nₓ<.... be a strictly increasing sequence of natural numbers.
Then the sequence X'=x(nₓ) given by {x(n₁),...,x(nₓ),..} is a subsequence of X.
Subsequences of convergent sequences also converge to the same limit
If a sequence X=x(n) of real numbers converges to a real number x, then any subsequence X'=x(nₓ) of X also converges to x.
Divergence Criteria

If a sequence X=x(n) of real numbers has either of these properties then X is divergent
(1)X has 2 convergent subsequences X'=x(nₓ) and X"=x(rₓ) whose limits are not equal.
(2)X is unbounded.
Monotone Subsequence Theorem
If X=x(n) is a sequence of real numbers, then there is a subsequence of X that is monotone.
Bolzano-Weierstrass Corollary
A bounded sequence of real numbers has a convergent subsequence.
Nested Intervals Proof
- intervals are nested, then I(n)⊆I(1) for all n∈N so a(n)≤b(n) for all n∈N
- there is a nonempty set {a(n):n∈N} that is bounded above
- let ξ be its supremum
- then a(n)≤ξ for all n∈N
- claim ξ≤b(n) for all n∈N
Case1: If n≤k, with I(n)⊇I(k), then a(k)≤b(k)≤b(n)
Case2: If k<n, with I(k)⊇I(n), then a(k)≤a(n)≤b(n)
-therefore, a(k)≤b(n) for all k, so b(n) is upper bound for set {a(k):k∈N}
-ξ≤b(n) for each n∈N
-a(k)≤ξ≤b(n) for all n which means ξ∈I(n) for all n∈N
If a>b and b>c then a>c
If a-b∈P and b-c∈P then (a-b)+(b-c)=(a-c)∈P
therefore a>c
If a>b then a+b>b+c
If a-b∈P then (a+c)-(b+c)=(a-b)∈P
If a>b and c>0 then ca>cb.
If a-b∈P and c∈P then ca-cb=c(a-b)∈P
therefore ca>cb when c>0
If a>b and c<0 then ca<cb.
If c<0, then -c∈P so that cb-ca=(-c)(a-b)∈P
therefore cb>ca when c<0
Completeness Property of R
Every nonempty set of real numbers that has an upper bound also has a supremum in R.
Limit of a sequence
A sequence X=x(n) in R is said to converge to x∈R, or x is a limit of x(n), if for every ε>0 ∃ a natural number K(ε) s.t. for n≥K(ε), the terms x(n) satisfy ∣x(n)-x∣<ε
Uniqueness of limits
A sequence in R can have at most 1 limit
Prove Uniqueness of limits
Suppose lim(x(n))=X' and X". For each ε>0 ∃ K' s.t. ∣x(n)-X'∣<ε/2 for all n≥K' and ∃ K" s.t. ∣x(n)-X"∣<ε/2 for all n≥K". Let K be the larger of K' and K". Then for n≥K, with the Triangle Inequality,
Since ε>0 then X'-X"=0
Limit Theorems: X+Y
Let X=x(n) and Y=y(n) be sequences of real numbers that converge to x and y
sequence X+Y converges to x+y
Limit Theorems: X-Y
Let X=x(n) and Y=y(n) be sequences of real numbers that converge to x and y
sequence X-Y converges to x-y
Limit Theorems: X*Y
Let X=x(n) and Y=y(n) be sequences of real numbers that converge to x and y
sequence X*Y converges to xy
Limit Theorems: cX
Let X=x(n) be sequence of real numbers that converge to x and let c∈R
sequence cX converges to cx
Squeeze Theorem
Suppose X=x(n), Y=y(n) and Z=z(n) are sequences of real numbers s.t. x(n)≤y(n)≤z(n) for all n∈N and the lim(x(n))=lim(z(n)).
Then Y=y(n) is convergent and lim(x(n))=lim(y(n))=lim(z(n))
Monotone Sequence
X=x(n) is a sequence then X is monotone if it either increases or decreases
Bolzano-Weierstrass Theorem
If an infinite set S is contained in a finite interval [a,b] then the set S has at least 1 limit point A in the interval [a,b]
Limit Point
A number x s.t. for all ε>0, ∃ a member of set y, different from x, s.t. ∣y-x∣<ε