How statement and proof provenance work
The first chip identifies the source of the statement or construction; the second identifies the source of its local proof or verification.
- Literature-sourced: the exact statement appears in a cited source; only wording and notation differ.
- AI-adapted: a semantically identical restatement of literature-sourced material, modulo indexing, notation, and boundary cases adopted by the library.
- AI-generated: a genuinely novel statement formulated by AI, with no source for the claim itself.
These labels describe origin, not correctness: citations and verification chips remain separate evidence.
Standard Maclaurin expansions
Statement
The standard Maclaurin expansions are
and
with value at . For every real ,
where
Facts & Assumptions
Given: The functions and power series displayed in the statement, and an arbitrary real parameter for the generalized-binomial family.
The Maclaurin series of a smooth function is (Taylor and Maclaurin series).
For , the geometric series satisfies (For , , and for the series diverges).
For every real , , and (The real exponential function and the number by a power series); and , (Sine and cosine defined by their real power series). The first definition names and names only as ; it does not name .
For , ; at the sum is , and at the series diverges ([The power series for log(1+x) on (-1,1], including the Abel endpoint](/item/thm-log-one-plus-x-power-series)).
For , , and the series at converges to (Principal arctangent: derivative, integral, power series, and the Gregory–Leibniz series).
For every real , is continuous on and has derivative there (Continuity and derivatives of positive-base real powers).
Factorials satisfy (The factorial and the falling factorial , defined by recursion in ), and for reals and a natural number the finite binomial theorem is (The binomial theorem in : ), the coefficients being the natural numbers read in through the canonical embedding. The exponents there are the natural-number ones: for every real , is the unique function on with and (Integer powers ).
If a sequence has no zero terms and , then converges absolutely (Ratio test: gives absolute convergence and hence convergence, and gives divergence).
A real power series may be differentiated term by term at every point inside its radius of convergence, and the differentiated series has the same radius (Inside its radius a real power series may be differentiated term by term, and the differentiated series has the same radius).
Sums and products of differentiable functions satisfy the sum and product rules (Sums, scalar multiples, products and quotients: , , , and when ).
If a real-valued function is continuous on an order-convex interval and has derivative zero at every interior point, then it is constant (A function continuous on an interval whose derivative vanishes at every interior point of is constant on ; consequently two such functions with the same derivative differ by a constant).
For naturals , ; consequently, as a real number, ( for ; hence , the quotient is a natural number, and ).
If is differentiable at a limit point of its domain and is differentiable at , itself a limit point of the domain of , then is differentiable at and (The chain rule, in one line from Carathéodory: if is differentiable at and is differentiable at , then is differentiable at with ).
For a natural the function is differentiable at every real with derivative , and for it is the constant , with derivative ; consequently every polynomial function is differentiable at every real, with the derivative computed term by term (For a natural the function is differentiable everywhere with derivative ; for it is the constant , with derivative ; for a natural the function is differentiable at every with derivative ; consequently every polynomial function is differentiable at every real, with the derivative computed term by term).
A function differentiable at a limit point of its domain is continuous at (A function differentiable at is continuous at ).
For and , (Real powers for positive bases, with the zero-base positive-exponent convention); is the inverse of , so for every real and for every (The natural logarithm as the inverse of the exponential function); and for and , (The exponent, product, quotient, and iterated-power laws for positive real bases and real exponents).
is a bijection (The exponential is a continuous bijection from onto ); in particular every value of is positive.
A real power series about the centre is , where the powers are those of Integer powers and convergence is that of Series, partial sums, convergence and the sum, divergence, and the tail series; at it always converges to , the term being because and every later term being ; and its radius of convergence is the supremum, in , of the such that the series converges absolutely at every with (A real power series about a centre, its interval of convergence, and its radius in ).
, and wherever is differentiable; is smooth, that is , on an interval when every exists there and is continuous there (Higher derivatives and the classes and ).
For naturals , is the number of -element subsets of ; in particular for every , and for (The set of -element subsets and the binomial coefficient ).
If and converge and is real, then converges to , and converges to (Convergent series add and scale termwise).
A real sequence converges to a real if and only if its limit inferior and its limit superior are both (A real sequence converges to iff , and diverges to iff both equal ).
If and then , , and (Algebra of limits: sums, scalar multiples, products and quotients); and for every there is a natural with (For every in a complete ordered field there is a natural with ).
A real power series of radius converges absolutely at every with and diverges at every with (A real power series converges absolutely inside its radius and diverges outside it, while either behaviour may occur at an endpoint).
Proof
The geometric, sine, cosine, logarithmic, and inverse-tangent identities, with exactly the displayed domains and endpoint assertions, are [L2]–[L5]. The exponential identity needs one further move, because the statement writes , the real power of the base in the sense of [L16], while [L3] defines and defines only as . By [L17] every value of is positive, so and [L16] assigns the value . Since is the inverse of [L16], , so and the series [L3] gives for is therefore the series of .
Suppose for with ; this is a power series about in the sense of [L18], and the hypothesis is exactly that it converges, with sum , at every with . Its radius of convergence is therefore at least : by [L24] a power series diverges at every point farther from its centre than its radius, so a point of convergence has , and letting run over gives . Every point of thus lies strictly inside the radius, so by [L9] the sum is differentiable there and its derivative is again a power series of radius ; induction on , using from [L7] at each step, gives for every , each again a power series about of radius . Evaluating at the centre, [L18] gives . Every is differentiable on , hence continuous there by [L15], so is smooth on in the sense of [L19] and [L1] applies at : the Maclaurin series of is . A power series representing near is therefore its Maclaurin series.
Fix and define and for .
On , the function is differentiable and has derivative . The inner map is a polynomial, so by [L14] it is differentiable with derivative at every point of , each of which is a limit point of ; its value lies in and is a limit point of , where by [L6] the outer map is differentiable with derivative . The chain rule [L13] therefore gives the composite derivative .
If is a nonnegative integer, the recurrence of step 1.3 gives for and for . Indeed by [L20]; and if and as a real number by [L12], then, since and with , while , after which the recurrence keeps every term . Taking and in the finite binomial theorem of [L7] then gives using for every natural , which the recursion , of [L7] gives by induction, and using for . The exponent in is there the natural-number one of [L7]. For that value is also the real power of [L16]: since , the real powers with satisfy , the value being the value at the centre of the series [L3] gives for , by [L18]; and, by the addition law of [L16] together with , also . That is the recursion determining the natural-number powers in [L7], so the two readings of agree.
Suppose is not a nonnegative integer and . Then, by step 1.3, and no factor of the recurrence vanishes, so every is nonzero, and ; the ratios are therefore defined. For every one has and hence so, since by [L23] and convergence of a sequence is a condition on its tails, [L23] gives . By [L22] the limit superior is that same limit, so and [L8] makes converge absolutely.
Thus the six series in step 1.1 are precisely the asserted Maclaurin expansions; the logarithmic and inverse-tangent endpoint values are values of the same series, not claims of an open interval beyond its radius.
Therefore, for every real , the power series built from step 1.3 converges absolutely at every with : when is a nonnegative integer every term past index vanishes by step 2.1 and the series is a finite sum; at it converges to by [L18]; and every remaining case is step 2.2. Its radius of convergence in the sense of [L18] is therefore at least .
By [L9] and step 3.1, is differentiable on with , again a power series of radius at least . The recurrence of step 1.3 gives , so for . Both and converge there, the first by step 3.1 and the second because it is , so [L21] splits the sum termwise into . Hence , that is , for .
For , both factors are differentiable on by step 1.4 and step 4.1, so the product rule gives there. On the base is positive, so and the addition law at the real exponents and gives , both by [L16]. Multiplying the displayed derivative by and using from step 4.1 therefore gives ; since , throughout .
Step 5.1 makes differentiable at every point of , and every such point is a limit point of , so [L15] makes continuous on .
The interval is order-convex, so [L11] and step 6.1 make constant there, and its constant value is . Here by [L18], the value of a power series at its centre being its constant coefficient, and by step 1.3. And is a real power of the base , so [L16] makes it , where is the value at the centre of the series [L3] gives for , by [L18], hence and . The constant value is therefore , that is for every . Multiplying by the real power and using the addition law of [L16] at the real exponents and , which gives , yields for every .
By step 1.2, applied to on , this is the Maclaurin expansion of ; its coefficients are the recursively defined numbers of the statement. That notation extends the library's binomial coefficient rather than clashing with it: when is a nonnegative integer, step 2.1 identifies with the count of [L20]. The argument makes no assertion at or .
Combining steps 2.3 and 8.1 proves all the displayed expansions with no additional endpoint claims.
Remarks
Which symbol is which. Three symbols in the statement name objects the library builds separately, and each is matched to its own definition rather than to a near neighbour.
is the real power of Real powers for positive bases, with the zero-base positive-exponent convention, not the series that defines : The real exponential function and the number by a power series defines and defines only as . Step 1.1 supplies the bridge, from .
The exponent in is real, so that power too is , whereas the exponent in the finite binomial theorem is a natural number and the appearing there is the integer power of Integer powers . Step 2.1 proves the two readings agree on ; without that they are different functions with the same name.
For real the symbol is defined by the recurrence in the statement, while elsewhere in the library is a count (The set of -element subsets and the binomial coefficient ). Step 2.1 proves the recurrence reproduces the count at a nonnegative integer , so the notation extends rather than overloads.
Two power conventions coexist here without conflict, and it is worth saying which is used where. The integer power fixes , which is what makes a power series equal its constant coefficient at the centre; the real power leaves undefined and is only ever applied above to bases , , and .
Depends on
- Taylor and Maclaurin series
- For $|r| < 1$, $\sum_{k \ge 0} r^k = 1/(1-r)$, and for $|r| \ge 1$ the series diverges
- The real exponential function and the number $e$ by a power series
- Sine and cosine defined by their real power series
- The power series for log(1+x) on (-1,1], including the Abel endpoint
- Principal arctangent: derivative, integral, power series, and the Gregory–Leibniz series
- Continuity and derivatives of positive-base real powers
- The factorial $n!$ and the falling factorial $n^{\underline{k}}$, defined by recursion in $\mathbb{N}$
- The binomial theorem in $\mathbb{R}$: $(x+y)^{n} = \sum_{k<n+1} \iota\!\binom{n}{k}\, x^{k} y^{\,n-k}$
- $\binom{n}{k}\,k!\,(n-k)! = n!$ for $k \le n$; hence $\binom{n}{k}\,k! = n^{\underline{k}}$, the quotient $n!/(k!(n-k)!)$ is a natural number, and $\binom{n}{k} = \binom{n}{n-k}$
- The set $[A]^{k}$ of $k$-element subsets and the binomial coefficient $\binom{n}{k} := \lvert [n]^{k}\rvert$
- Ratio test: $\limsup |a_{k+1}/a_k| < 1$ gives absolute convergence and hence convergence, and $\liminf |a_{k+1}/a_k| > 1$ gives divergence
- Inside its radius a real power series may be differentiated term by term, and the differentiated series has the same radius
- Sums, scalar multiples, products and quotients: $(f+g)'(c) = f'(c) + g'(c)$, $(\alpha f)'(c) = \alpha f'(c)$, $(fg)'(c) = f'(c)g(c) + f(c)g'(c)$, and $(f/g)'(c) = \bigl(f'(c)g(c) - f(c)g'(c)\bigr)/g(c)^{2}$ when $g(c) \ne 0$
- For a natural $n \ge 1$ the function $x \mapsto x^{n}$ is differentiable everywhere with derivative $\iota(n)\,x^{\,n-1}$; for $n = 0$ it is the constant $1$, with derivative $0$; for a natural $n \ge 1$ the function $x \mapsto x^{-n}$ is differentiable at every $x \ne 0$ with derivative $-\iota(n)\,x^{-n-1}$; consequently every polynomial function is differentiable at every real, with the derivative computed term by term
- The chain rule, in one line from Carathéodory: if $g$ is differentiable at $c$ and $f$ is differentiable at $g(c)$, then $f \circ g$ is differentiable at $c$ with $(f \circ g)'(c) = f'(g(c))\,g'(c)$
- A function differentiable at $c$ is continuous at $c$
- Real powers for positive bases, with the zero-base positive-exponent convention
- The natural logarithm as the inverse of the exponential function
- The exponent, product, quotient, and iterated-power laws for positive real bases and real exponents
- Integer powers $a^m$
- A function continuous on an interval $I$ whose derivative vanishes at every interior point of $I$ is constant on $I$; consequently two such functions with the same derivative differ by a constant
- The exponential is a continuous bijection from $\mathbb{R}$ onto $(0,\infty)$
- A real power series about a centre, its interval of convergence, and its radius in $[0,+\infty]$
- A real power series converges absolutely inside its radius and diverges outside it, while either behaviour may occur at an endpoint
- Series, partial sums, convergence and the sum, divergence, and the tail series
- Higher derivatives and the classes $C^k$ and $C^\infty$
- Convergent series add and scale termwise
- A real sequence converges to $L \in \mathbb{R}$ iff $\liminf x_k = \limsup x_k = L$, and diverges to $\pm\infty$ iff both equal $\pm\infty$
- Algebra of limits: sums, scalar multiples, products and quotients
- For every $\varepsilon > 0$ in a complete ordered field there is a natural $n \ge 1$ with $1/n < \varepsilon$
Used by
Nothing in the library uses this result yet.
Dependency tree · next 3 levels
Direct dependencies and their dependencies through the next three levels: 265 results over 45 levels. An arrow runs from a result to what uses it, and this result sits at the bottom with a heavier outline. Click the chart to enlarge it.
Sources
- W. F. Trench, Introduction to Real Analysis, §4.5, pp. 265–267 (standard reference, not scraped)
- MIT OpenCourseWare 18.100C Real Analysis, Lecture 23 (standard reference, not scraped)