Functions Concepts
76 concepts · Grades 6-8, 9-12 · 106 prerequisite connections
This family view narrows the full math map to one connected cluster. Read it from left to right: earlier nodes support later ones, and dense middle sections usually mark the concepts that hold the largest share of future work together.
Use the graph to plan review, then use the full concept list below to open precise pages for definitions, examples, formulas, and related mistake guides. That combination keeps the page useful for both human study flow and crawlable internal linking.
Concept Dependency Graph
Concepts flow left to right, from foundational to advanced. Hover to highlight connections. Click any concept to learn more.
Connected Families
Functions concepts have 55 connections to other families.
All Functions Concepts
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.
Domain
The domain of a function is the complete set of allowable input values for which the function produces a defined, valid output.
Range
The range of a function is the set of all actual output values that the function can produce for inputs in its domain.
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.
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.
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.
Logarithm
The logarithm $\log_b(x)$ answers: "to what power must $b$ be raised to produce $x$?" It is the inverse function of $f(x) = b^x$.
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.
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.
Periodic Functions
A periodic function repeats its values at regular intervals: $f(x + T) = f(x)$ for all $x$, where $T > 0$ is the period — the length of one complete cycle.
Polynomial Functions
Functions made by adding terms of the form $ax^n$ (where $n$ is a non-negative integer).
Rational Functions
A rational function is a ratio of two polynomials: $f(x) = P(x)/Q(x)$ where $P$ and $Q$ are polynomials and $Q(x) \neq 0$.
Asymptote
An asymptote is a line that a curve approaches arbitrarily closely as the input (or output) grows without bound, but typically never reaches.
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.
Function Transformation
A function transformation shifts, stretches, compresses, or reflects the graph of a parent function by modifying its formula in a systematic way.
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.
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.
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.
Multiple Representations
The different ways to express the same function: formula, table, graph, or words.
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.
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.
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.
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.
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.
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.
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.
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.
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.
Feedback
Feedback occurs when the output of a system influences its future input — positive feedback amplifies changes; negative feedback stabilizes them.
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.
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.
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.
Functional Modeling
Functional modeling uses functions to represent relationships between real-world quantities — choosing the right function family to capture the observed pattern.
Dependency Graphs
A dependency graph is a directed graph where nodes are variables and arrows show which variables directly influence which others.
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 $k$.
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).
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.
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.
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.
Unit Circle
The circle of radius 1 centered at the origin in the coordinate plane, used to define trigonometric functions for all angles.
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.
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.
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.
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 $1 + \cot^2\theta = \csc^2\theta$.
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 $\cos B$.
Double-Angle Identities
Formulas expressing $\sin(2\theta)$, $\cos(2\theta)$, and $\tan(2\theta)$ in terms of single-angle trig functions.
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 $e^x$.
Change of Base Formula
A formula for converting a logarithm from one base to another: $\log_b x = \frac{\ln x}{\ln b} = \frac{\log x}{\log b}$.
Solving Exponential Equations
Using logarithms to solve equations where the unknown is in the exponent, such as $a^x = b$.
Solving Logarithmic Equations
Solving equations containing logarithms by converting to exponential form or using log properties to combine and simplify.
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.
Ellipse
The set of all points in a plane where the sum of the distances to two fixed points (foci) is constant. Standard form: $\frac{(x-h)^2}{a^2} + \frac{(y-k)^2}{b^2} = 1$.
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.
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).
Conic Sections Overview
The four curves—circle, ellipse, parabola, and hyperbola—obtained by slicing a double cone with a plane at different angles.
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 $(r, \theta)$.
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.
Parametric Equations
A way of defining a curve by expressing both $x$ and $y$ as separate functions of a third variable (parameter), typically $t$: $x = f(t)$, $y = g(t)$.
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.
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.
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.
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.
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.
Planes in 3D
A flat, infinite surface in three-dimensional space described by the equation $ax + by + cz = d$, where the vector $\langle a, b, c \rangle$ is normal (perpendicular) to the plane.
Function Notation
Function notation writes outputs as $f(x)$ to show a rule assigning each input to an output.
Symmetric Functions
Symmetric functions are unchanged under specific variable swaps or sign transformations.
Restricted Domain
Restricting a domain limits allowable inputs so a function has desired properties, often invertibility.
Horizontal Line Test
A graph passes the horizontal line test if every horizontal line intersects it at most once.
Amplitude
Amplitude is the maximum vertical distance from the midline of a periodic function to a peak or trough.
Frequency
Frequency is the number of complete cycles of a periodic process per unit of input (often time).
Parent Functions
A parent function is the simplest base graph in a function family before transformations.
Exponential Growth
Exponential growth occurs when a quantity increases by a constant multiplicative factor over equal intervals.
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).
Radians
A radian measures angle by arc length: one radian subtends an arc equal to the circle radius.