MindMap Gallery Chapter 1 Function Limit Continuity Knowledge Points
Wu Zhongxiang’s course study notes mainly include supplementary knowledge, Easy to confuse and error, continuity of nodal functions, limits, etc. Use it for review and preview, double your efficiency! If you need it, collect it quickly!
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Chapter 1 Function Limit Continuity Knowledge Points
Supplementary knowledge
Multiple choice question skills
direct method
Exclusion
How to use
General function (only tells the conditions that f(x) satisfies, no expression for f(x))
When to use
f(x) represents a specific function (if the conditions are met, the simpler the better)
Factorization of cubic polynomials
Decomposed form
method
undetermined coefficient method
1. Set the coefficients according to the decomposition form
2. Compare the original polynomial with the set polynomial to get the coefficients
long division
1. Observe that a root of the polynomial x1
2. Polynomial/(x-x1) can get the quadratic factor of the polynomial
Simplify means
Radical (square root)
Numerator/denominator rationalization
Related formulas for trigonometric functions
Confusing and error-prone
I. Properties of continuous functions on closed intervals (not on open intervals)
II. Continuity and Limit
The relationship between the continuity of a function at a certain point and the limit at a certain point
f(x)(x->x0)=f(x0)=A (three meanings)
III. Domain and interval
example
Domain
All defined points (unique)
Define interval
An interval contained within the domain (not unique)
Section 2 Limit
1. concept of limit
Prerequisites for studying whether limits exist
Is f(x) defined in the neighborhood of x0 at a certain point ---> Discuss further only if it is defined
The limit of a sequence
Mathematical definition (two representations) P21
Notice
I. The role of ε and N
II. The geometric significance of the limit of a sequence
III. Whether the limit of the sequence exists or what the value of the limit is has nothing to do with the previous finite term of the sequence.
IV. The limit of the sequence exists<-->The limits of the odd and even subsequences exist and are equal
limit of function
Mathematical representation (two types) P28
Notice
I. The role of ε and δ
II. The geometric meaning of function limits
III. x->x0 but x≠x0 (P9)
IV. The limit at a certain point (bilateral) exists <-> the left limit and the right limit (two unilateral) exist and are equal
Two situations
The independent variable tends to infinity
Bilateral limit
The absolute value of the independent variable tends to infinity
One-sided limit
The independent variable tends to positive infinity or negative infinity
The independent variable tends to a finite value
left limit (symbol)
Right limit (symbol)
Describes a function approaching a certain point from left (right)
It is necessary to divide the left and right limits to find the limit
1. The piecewise function finds the limit at the dividing point, and the expressions on both sides of the dividing point are inconsistent.
2. e^∞ type
3. arctan∞ type
Function -∞ and ∞ limits are inconsistent
properties of limits
I. (Sequence) bounded but not necessarily convergent: (-1)^n
II. (Function) is locally bounded and does not necessarily converge: sin(1/n)
2. properties of limits
uniqueness
Boundedness
Convergence must be bounded; unbounded must be divergence
Number retention
3. The ultimate law of existence
Clamping Criterion
Mostly used for n terms and limits
monotonic bounded criterion
Mostly used in the recursive formula Xn 1 = f(Xn)
Monotonically increasing only proves that there is an upper bound (the first term of the sequence is the lower bound)
Monotone reduction only proves that there is a lower bound (the first term of the sequence is the upper bound)
If the first finite term does not satisfy it, it will not affect the use of the criterion.
4. Two extreme states of the limit
infinitesimal amount
concept
A variable with a limit of 0 (in a certain limit process)
0 is the only constant that can be infinitesimal
Comparison of infinitesimal quantities
Study the speed at which variables tend to 0 during a certain limit process
The relationship between limit values and infinitesimals
The bridge between functions and limits
infinite amount
concept
How big should the absolute value be (in a certain limit process)
infinite number of comparisons
Pair, power, index, factorial, power index (small->large)
vertical asymptote
When the function approaches a certain point, the limit tends to infinity --> This point is the vertical asymptote of the function graph.
relation
extreme algorithm
infinitesimal amount
The sum of a finite number of infinitesimals is still infinitesimal
Counterexample P13 (infinite sums of infinitesimals)
The product of a finite number of infinitesimals is still infinitesimal
The product of an infinitesimal quantity and a bounded quantity is still infinitesimal
xsin(1/x) (x->0)
infinite amount
The product of finite infinities is still infinite
Limit arithmetic rules for composite functions
The inner layer has limits
The outer layer has limits
The function value of the inner function cannot be equal to u0
5. unbounded variable
nature
Unbounded × Unbounded does not necessarily mean unbounded
The product of unbounded and bounded variables is still an unbounded variable
The product of infinity and unbounded variables is not necessarily infinite (n*sin(1/n))
Relationship with infinite quantitiesP13
The sum of an infinite quantity and an unbounded variable is infinite
infinite amount
sequence
For any M>0, there exists N>0. When n>N, there is always |Xn|>M
function
In a certain limit process, the function value can be greater than any given M>0
unbounded variable
sequence
For any M>0, there exists N>0, and when n>N, there is |Xn|>M
function
On the interval I, there is a point x0, so that the value of the function should be as large as possible
Infinite quantities are more stringent than unbounded variable conditions
6. Seeking the limit (proficient in the method)
i. Simplification
The limit is equal to a non-zero constant factor --> Calculate and mention lim
factoring
Can be factorized first by factoring-->Generally, non-zero constant factors can be calculated
Use the four arithmetic rules of limit-->the limit is equal to the non-zero constant factor and calculate first
ii. method
Use basic limits to find limits
1. The Limit of Polynomial Fractions (Catch the Boss)
Find the limit using equivalent infinitesimal substitutions
Find limits using rational arithmetic rules
The denominator limit is 0--->Zero factor elimination method--->Operation rule of quotient
Find the limit using Lópida's law
Conditions of Use
Find the limit using Taylor's formula
The meaning of Taylor's formula
I. Establish a bridge between f(x) and f(x)n-order derivatives
II. Approximating f(x) with polynomials
III. Polynomial solution (integration, limit, derivative) is simple
Basic Taylor formula
5 basic Taylor formulas (memorized)
3 derivation can lead to Taylor formula
The existence criterion of limit
Use the pinching principle to find limits
Limit of sequence for sum of n terms
Zoom in or out
enlarge
Take the smallest of all denominators
zoom out
Take the largest of all denominators
Observe the formula to find the upper and lower bounds and then squeeze them (P12 Example 8)
P23 Example 39 (Important Conclusion)
Find the limit using the monotonic bounded criterion
Recurrence relationship Xn 1= f(Xn)
step
1. Existence (monotone bounded)
Monotonicity proof
Anterior term than posterior term
Antecedent minus consequent
Proof of boundedness
basic inequalities
2. a= f(a) (take the limit on both sides simultaneously)
Find limits using definite integrals
Section 3 Continuity of Functions
I. Section 1 Function
1. The concept of function and common functions
The concept of function
Domains and Correspondence Rules
piecewise function
Symbol function sgnx
rounding function
Common functions
Composite function
condition
The domain of the outer function ∩ the value domain of the inner function ≠∅
function solver
expression
Domain
Inverse function
condition
For any y belonging to Rf, there is a unique x∈D (one-to-one mapping)
Notice
The relationship between monotonic functions and inverse functions
The relationship between inverse function and original function
elementary functions
basic elementary functions
The relationship between piecewise functions and elementary functions
definition
The construction of elementary functions
and can be expressed as a function
2. Properties of functions (four basic forms)
premise
Discuss on the interval I (if no specific interval is specified, discuss on the definition domain)
To discuss derivative functions (functions that are differentiable) and original functions (functions that are continuous), you need to first determine whether they exist
Monotonicity
Strictly monotonic increasing (without equal sign) and monotonic non-decreasing (with equal sign)
determination
definition
Derivative function>0 --->The function is monotonically increasing (sufficient condition)
Derivative function ≥ 0 <---> The function is monotonic and does not decrease (necessary and sufficient condition)
Parity
The domain is symmetric about the origin
If f(0) exists as an odd function, then f(0)=0
determination
definition
Function odd function (original function of derivative function)<--->Even function of derivative function (necessary and sufficient conditions)
Function evenness (original function of derivative function) --->Odd function of derivative function
cyclical
Periodic function Any constant is still a periodic function
determination
Periodic function (differentiable)--->The derivative function is a periodic function (sufficient condition)
Periodic function (continuous)--//-->The original function is a periodic function
Periodic function (continuous) The integral over a period is 0--->The original function is a periodic function
Boundedness
Bounded, unbounded
determination
f(x) is continuous on [a,b]-->f(x) is bounded on [a,b]
f(x) is continuous on (a,b) and the one-sided limit of the interval endpoint exists-->f(x) is bounded on (a,b)
The derivative function is bounded on the interval I (finite) --->f(x) is bounded on I (key point)
II. concept of continuity
point
definition
1. When the independent variable increment is 0, the corresponding function value increment is 0
2. The limit of a function exists at a certain point and the limit value = the function value at that point (three meanings)
equivalence
the difference
function limit
Study the changing trend of function values adjacent to a certain point of the function
function continuous
Study the relationship between the changing trend of adjacent points and the function value of the point
interval
Open interval (a,b)
The function is continuous within the interval
Closed interval [a,b]
The function is continuous within the interval
The function is continuous at the endpoints
Left endpoint right continuous
Right endpoint left continuous
III. Discontinuity points and their classification
Discussion premise
The function is defined in a certain decentered neighborhood of the discontinuity point
break point definition
The function is defined in a certain decentered neighborhood of a certain point, but is discontinuous at x0
Discontinuities of the first kind
definition
Discontinuity points that exist in both left and right limits
Classification
Can remove discontinuities
definition
left=right
By redefining the point function value, the discontinuous point can be removed
jump break point
definition
left ≠ right
When passing this point, the function graph jumps
Type II discontinuities
definition
There is at least one non-existent discontinuity point in the left and right limits
Classification
infinite discontinuity
Oscillation break point
When the function approaches a certain point, the function value changes infinitely many times in a certain interval.
other
IV. Operations and properties of continuous types
1. The sum, difference, product, and quotient of continuous functions (denominator ≠ 0) are still continuous functions
2. The composition of a continuous function is still a continuous function
3. Basic elementary functions are continuous within their domain
4. An elementary function is continuous within its defined interval
5. Notice
basic elementary functions
continuous within the domain of definition
If there is a definition point, it must be continuous
elementary functions
Continuous within the definition interval (interval included in the definition domain)
Even if there are defined points, they are not necessarily continuous (discrete points). It needs to be judged whether they are within the defined interval.
V. Properties of continuous functions on closed intervals
Maximum value theorem
boundedness theorem
Intermediate value theorem
zero point theorem
Prove the existence of the roots of the equation
VI. question type
concept of continuity
When do we need to discuss left and right continuity (left and right are different)
Piecewise function breaking point
The expressions on the left and right sides of this point are different
Discontinuity points and their classification
How to find discontinuities
Function has no definition point
Discrimination of discontinuity points
The first type of discontinuity point needs to be explained: you can jump to OR
There is no need to specify which type of discontinuity point of the second type
Types of Continuities and Discontinuities
Possible discontinuities
1. Function has no definition
The denominator is 0
2. The expressions on the left and right sides of the click are different
piecewise function piecewise point
3. The limits on the left and right sides of the click are different
continuous points
The function is defined at this point
The function has a limit at this point
The limit value of the function at this point = function value
Notice
basic elementary functions
continuous within the domain of definition
If there is a definition point, it must be continuous
elementary functions
Continuous within the definition interval (interval included in the definition domain)
Even if there are defined points, they are not necessarily continuous (discrete points). It needs to be judged whether they are within the defined interval.