Advanced Functions
76 concepts · ordered by prerequisite depth
Functions are the central organizing idea of modern mathematics. A function describes a precise relationship where each input produces exactly one output — a concept that unifies algebra, geometry, and data analysis. In this advanced topic, students move beyond linear functions to explore polynomial, rational, exponential, logarithmic, and trigonometric functions. They learn to analyze functions through multiple representations: equations, tables, graphs, and verbal descriptions. Key skills include identifying domain and range, composing functions, finding inverses, and recognizing transformations such as shifts, stretches, and reflections. Understanding function behavior — where a function increases, decreases, or changes concavity — lays the groundwork for calculus. These concepts are indispensable in modeling real-world phenomena from population growth to sound waves.
Suggested order: Build on linear function knowledge by studying quadratics and polynomials, then progress to exponential and logarithmic functions, and finally explore trigonometric functions and function composition.
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Function
A function is a rule that assigns to each input in the domain exactly one output in the codomain — every input maps to precisely one output, never two.
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Domain
The domain of a function is the complete set of allowable input values for which the function produces a defined, valid output.
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Inverse Function
The inverse of a function $f$ is a function $f^{-1}$ that reverses $f$: if $f(a) = b$ then $f^{-1}(b) = a$. It exists only when $f$ is one-to-one.
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Continue from here · 73 concepts
Changing Rate
A changing rate of change means the output grows by different amounts for equal increases in input — the hallmark of nonlinear functions like quadratics and exponentials.
Constant Rate
A constant rate of change means the output increases (or decreases) by the same fixed amount for every unit increase in the input — the hallmark of a linear function.
Dependency Graphs
A dependency graph is a directed graph where nodes are variables and arrows show which variables directly influence which others.
Parabola (Focus-Directrix Definition)
A parabola is the set of all points equidistant from a fixed point (the focus) and a fixed line (the directrix).
Polynomial Functions
A polynomial function is formed by adding terms of the form $ax^n$ where $n$ is a non-negative integer. The highest power determines the degree, which controls the graph's end behavior, maximum turning points, and number of possible real zeros.
Proportional Function
A proportional function has the form $f(x) = kx$ for a constant $k \neq 0$ — it passes through the origin and the ratio $f(x)/x = k$ is constant.
Sensitivity
In the context of functions, sensitivity measures how much the output changes in response to a small change in the input — high sensitivity means small input changes cause large output changes.
Trigonometric Functions
Trigonometric functions (sin, cos, tan, etc.) relate angles in right triangles to side ratios and extend to periodic functions of real numbers via the unit circle.
Asymptote
An asymptote is a line that a curve approaches arbitrarily closely as the input (or output) grows without bound, but typically never reaches.
Continuous Function
A function is continuous at a point if the limit equals the function value there, with no jumps, holes, or vertical asymptotes in the interval of interest.
Exponential Function
An exponential function has the form $f(x) = a \cdot b^x$ where $b > 0$, $b \neq 1$. The variable is in the exponent, not the base.
Function as Mapping
Viewing a function as a mapping means thinking of it as an explicit association from each element of the domain to exactly one element of the codomain.
Function Composition
Function composition applies one function to the output of another: $(f \circ g)(x) = f(g(x))$, meaning evaluate $g$ first, then apply $f$ to the result.
Function Families
A function family is a group of functions sharing the same general form and behavior, differing only in the values of one or more parameters.
Function Notation
Function notation $f(x)$ is a shorthand that names a function ($f$) and specifies its input ($x$). Writing $f(3) = 10$ means that when the input is 3, the function produces the output 10. This notation is not multiplication.
Function Transformation
A function transformation shifts, stretches, compresses, or reflects the graph of a parent function by modifying its formula in a systematic way.
Functional Modeling
Functional modeling uses functions to represent relationships between real-world quantities — choosing the right function family to capture the observed pattern.
Input-Output View
The input-output view of a function treats it as a black box: put in a value (input), get out a uniquely determined value (output), without worrying about the internal mechanism.
Local vs Global Behavior
Local behavior describes a function's properties near a specific point; global behavior describes its overall properties across the entire domain or as inputs grow without bound.
Many-to-One Mapping
A many-to-one function maps multiple distinct inputs to the same output — it is a valid function (each input still has exactly one output) but has no inverse.
Multiple Representations
Every function can be expressed in four equivalent ways: as an algebraic formula, a table of input-output pairs, a graph on the coordinate plane, or a verbal description. Each representation highlights different properties and is useful in different contexts.
One-to-One Mapping
A one-to-one (injective) function maps every distinct input to a distinct output — no two different inputs produce the same output.
Parametric Equations
A way of defining a curve by expressing both $x$ and $y$ as separate functions of a third variable (parameter), typically $t$: $x = f(t)$, $y = g(t)$.
Periodic Functions
A function that repeats its values at regular intervals: $f(x + T) = f(x)$ for all $x$, where $T$ is the smallest positive period.
Rational Functions
A rational function is a ratio of two polynomials: $f(x) = P(x)/Q(x)$ where $P$ and $Q$ are polynomials and $Q(x) \neq 0$.
Stability
A system is stable at an equilibrium if small perturbations cause it to return toward that equilibrium; unstable if small perturbations cause it to move away.
Unit Circle
The circle of radius 1 centered at the origin in the coordinate plane, used to define trigonometric functions for all angles.
Composition Chains
A composition chain is a sequence of functions applied one after another: $(f \circ g \circ h)(x) = f(g(h(x)))$, evaluated inside-out from right to left.
Equation of a Circle
The standard form equation $(x - h)^2 + (y - k)^2 = r^2$ describes a circle with center $(h, k)$ and radius $r$ in the coordinate plane.
Euler's Number
Euler's number $e \approx 2.71828$ is the unique base for which the exponential function $e^x$ is its own derivative — the natural base for growth and decay.
Feedback
Feedback occurs when the output of a system influences its future input — positive feedback amplifies changes; negative feedback stabilizes them.
Frequency
The number of complete wave cycles passing a fixed point per second, measured in hertz (Hz).
Growth vs Decay
Exponential growth occurs when a quantity multiplies by a factor $> 1$ repeatedly; exponential decay when it multiplies by a factor between 0 and 1.
Horizontal Line Test
The horizontal line test is a visual method to determine whether a function is one-to-one (injective). If every horizontal line intersects the function's graph at most once, the function passes the test and has an inverse function on its full domain.
Invariants Under Transformation
A property of a function is invariant under a transformation if it remains unchanged after the transformation is applied to the function.
Inverse Trigonometric Functions
Functions that reverse the trigonometric functions: given a ratio, they return the corresponding angle. $\arcsin$, $\arccos$, and $\arctan$ are the inverses of $\sin$, $\cos$, and $\tan$ on restricted domains.
Lines in 3D
Lines in three-dimensional space described using parametric equations $x = x_0 + at$, $y = y_0 + bt$, $z = z_0 + ct$, or symmetric form $\frac{x - x_0}{a} = \frac{y - y_0}{b} = \frac{z - z_0}{c}$, where $(x_0, y_0, z_0)$ is a point on the line and $\langle a, b, c \rangle$ is the direction vector.
Logarithm
The logarithm $\log_b(x)$ answers: "to what power must $b$ be raised to produce $x$?" It is the inverse function of $f(x) = b^x$.
Parametric Graphs
Plotting and analyzing curves defined by parametric equations $x = f(t)$, $y = g(t)$, including eliminating the parameter, determining direction of motion, and finding tangent lines.
Parent Functions
A parent function is the simplest, most basic version of a function family — the unshifted, unstretched, unreflected template. All other functions in the family are transformations of this parent. Memorizing parent function shapes allows rapid graphing of transformed versions.
Piecewise Function
A piecewise function is defined by different formulas on different non-overlapping intervals of its domain, with the applicable formula determined by the input value.
Pythagorean Trigonometric Identities
The fundamental identity $\sin^2\theta + \cos^2\theta = 1$ and its derived forms: $1 + \tan^2\theta = \sec^2\theta$ and $1 + \cot^2\theta = \csc^2\theta$.
Radian Measure
An angle measure defined by the arc length subtended on a unit circle: one radian is the angle that subtends an arc equal in length to the radius.
Radians
A radian is an angle measurement defined by the arc length it subtends on a unit circle: one radian is the angle at which the arc length equals the radius. A full circle is $2\pi$ radians (about 6.28 radians), making radians the natural unit for trigonometry and calculus.
Range
The range of a function is the set of all actual output values that the function can produce for inputs in its domain.
Reflecting Functions
Reflecting a function mirrors its graph across the $x$-axis ($-f(x)$), $y$-axis ($f(-x)$), or the line $y = x$ (the inverse function).
Restricted Domain
Restricting a domain limits allowable inputs so a function has desired properties, often invertibility.
Scaling Functions
Scaling a function multiplies its output by a constant (vertical scaling) or compresses/stretches its input (horizontal scaling), changing amplitude or period without changing the shape.
Shifting Functions
Shifting a function translates its graph horizontally or vertically without changing its shape: $f(x - h) + k$ shifts right by $h$ and up by $k$.
Trigonometric Function Graphs
The graphs of $\sin x$, $\cos x$, and $\tan x$ as functions of a real variable, characterized by amplitude, period, phase shift, and vertical shift.
Amplitude
Amplitude is the maximum vertical distance from the midline of a periodic function to a peak or trough.
Compound Interest
Interest calculated on both the initial principal and the accumulated interest from previous periods. The formula $A = P\left(1 + \frac{r}{n}\right)^{nt}$ gives the amount after $t$ years, and $A = Pe^{rt}$ gives the continuously compounded amount.
Ellipse
The set of all points in a plane where the sum of the distances to two fixed points (foci) is constant. Standard form: $\frac{(x-h)^2}{a^2} + \frac{(y-k)^2}{b^2} = 1$.
Even and Odd Functions
An even function satisfies $f(-x) = f(x)$ (symmetric about $y$-axis); an odd function satisfies $f(-x) = -f(x)$ (rotational symmetry about origin).
Hyperbola
The set of all points in a plane where the absolute difference of the distances to two fixed points (foci) is constant. The curve has two separate branches and asymptotes.
Logarithm Properties
The three fundamental rules of logarithms: the product rule $\log_b(xy) = \log_b x + \log_b y$, the quotient rule $\log_b\!\left(\frac{x}{y}\right) = \log_b x - \log_b y$, and the power rule $\log_b(x^n) = n\log_b x$.
Natural Logarithm
The logarithm with base $e \approx 2.71828$: $\ln x = \log_e x$. It is the inverse function of $e^x$.
Piecewise Behavior
Piecewise behavior refers to a function that exhibits qualitatively different characteristics in different regions of its domain, like having a different slope or curvature in each region.
Planes in 3D
A flat, infinite surface in 3D space described by $ax + by + cz = d$, where $\langle a, b, c \rangle$ is the normal vector.
Polar Coordinates
A coordinate system where each point in the plane is described by a distance $r$ from the origin and an angle $\theta$ from the positive $x$-axis, written as $(r, \theta)$.
Saturation
Saturation is the phenomenon where a growing quantity approaches a limiting value asymptotically, with the rate of growth decreasing as the limit is approached.
Step Function Intuition
A step function is piecewise constant — it takes a fixed value on each of several intervals, jumping abruptly at the interval boundaries.
Sum and Difference Identities
Formulas that express $\sin(A \pm B)$, $\cos(A \pm B)$, and $\tan(A \pm B)$ in terms of $\sin A$, $\cos A$, $\sin B$, and $\cos B$.
Symmetric Functions
A symmetric function is one that remains unchanged (or changes in a predictable way) under specific variable transformations. Even functions satisfy $f(-x) = f(x)$ and are mirror-symmetric about the y-axis; odd functions satisfy $f(-x) = -f(x)$ and have 180-degree rotational symmetry about the origin.
Annuities
A series of equal payments made at regular intervals over a fixed period of time. The future value and present value formulas calculate the total worth of these payment streams.
Change of Base Formula
A formula for converting a logarithm from one base to another: $\log_b x = \frac{\ln x}{\ln b} = \frac{\log x}{\log b}$.
Conic Sections Overview
The four curves—circle, ellipse, parabola, and hyperbola—obtained by slicing a double cone with a plane at different angles.
Double-Angle Identities
Formulas expressing $\sin(2\theta)$, $\cos(2\theta)$, and $\tan(2\theta)$ in terms of single-angle trig functions.
Exponential Growth
Exponential growth occurs when a quantity increases by a constant multiplicative factor over equal intervals.
Polar Graphs
Graphs of equations in the form $r = f(\theta)$, producing curves such as rose curves, cardioids, limaçons, and circles in the polar plane.
Present and Future Value
The concept that money has different values at different points in time. Future value ($FV$) calculates what a present amount will grow to; present value ($PV$) calculates what a future amount is worth today, using discounting.
Solving Exponential Equations
Solving exponential equations means finding the unknown variable trapped in an exponent by applying logarithms to both sides, using the power rule to bring the exponent down, and then isolating the variable with standard algebra.
Solving Logarithmic Equations
Solving equations containing logarithms by converting to exponential form or using log properties to combine and simplify.