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Mathematics & logicExamples and counterexamples

Learn what a claim covers, explain why it works, and recognise an allowed case that shows it needs changing.

Method
Mathematics & logicCounting and zero

Count each object once, explain the final count, and distinguish quantity, position and identifying labels. Make zero’s role explicit.

Definition
Mathematics & logicNumber lines and order

Use number-line positions to compare whole numbers. Read the scale, recognise equality, and distinguish numerical distance from drawing size.

Definition
Mathematics & logicAddition and subtraction

Combine separate counts, remove a part, and find differences or missing parts. Connect objects, equations and number-line moves, then use tens and ones to regroup without changing value.

Definition
Mathematics & logicMultiplication and division

Count equal groups, distinguish sharing from making groups, and check with multiplication. Split calculations into parts; interpret zero and remainders in context.

Definition
Mathematics & logicFractions

Choose a whole, count equal fractional units, and connect sharing with division. Place fractions on the number line, including values beyond one, and explain what their numerator and denominator mean.

Definition
Mathematics & logic · Physics · MeasurementRatios and rates

Distinguish part-to-part ratios, fractions of a whole and rates with units. Scale quantities together, compare unit rates, and explain when a relationship is proportional. Check zero cases, starting amounts and whether a result fits its context.

Definition
Mathematics & logic · Physics · MeasurementQuantities and units

Describe a quantity as a numerical value with a unit, and distinguish its physical kind from its dimension. Build length, area, volume and rate units, check meaningful combinations, and separate exact unit relations from measurement uncertainty.

Definition
Mathematics & logic · Physics · MeasurementUnit conversions

Convert quantities with exact unit ratios, track cancellation through compound units, and apply the correct powers to area and volume. Distinguish temperature readings from differences, check dimensions and context, and retain measurement uncertainty when reporting.

Method
Mathematics & logic · Physics · MeasurementEstimation and uncertainty

Distinguish exact model values, rounded approximations and estimates from measurements. Declare the rounding rule, preserve information through calculations and unit changes, and interpret resolution, precision, accuracy and the stated uncertainty type without turning a report’s digits into guaranteed bounds.

Definition
Mathematics & logicVariables and expressions

Use symbols to name numbers or quantities, describe their allowed values, and evaluate expressions by replacing every occurrence consistently. Preserve grouping, signs, fractions and units, and distinguish a calculated value from solving an equation or proving two rules equivalent.

Definition
Mathematics & logicEquality and equations

Read equality as a relationship, find the permitted values that make an equation true, and justify one-step solutions by reversible operations on both sides. Work exactly with negative numbers and fractions, recognize all-solution and no-solution cases, and check the original equation, units and context.

Definition
Mathematics & logic · PhysicsCoordinates and tables

Locate a point from an ordered pair, read named axes and their scales, and connect the same values in words, tables and plots. Keep signs, fractions and units exact, distinguish an axis point from a quadrant point, and separate selected observations from a stated rule and its domain before drawing connections.

Definition
Mathematics & logic · PhysicsSlope and straight lines

Read a straight line as a stated relationship, calculate its slope from consistent signed coordinate changes, and interpret its intersections with the axes. Keep horizontal, vertical and coincident-point cases distinct, attach units and domain conditions to context models, and use numerical scales rather than appearance alone to judge a line’s change.

Definition
Mathematics & logic · Physics · MeasurementReading graphs

Read a graph’s quantities, units, ticks and context before judging its visual impression. Calculate differences, reference-based percentages and interval rates from the represented values; distinguish legitimate zoom from distorted spacing; and keep samples, interpolation, missing information, uncertainty and causal explanations separate.

Method
Mathematics & logic · PhysicsApproximations

Build a useful estimate, compare a correction with a stated reference scale, and check what is lost when you leave out a term.

Approximation
Mathematics & logic · PhysicsSymmetry and invariance

Specify a transformation, identify what stays unchanged, and distinguish symmetry of an object from invariance of a physical model.

Mathematical statement
Mathematics & logic · PhysicsVectors

Describe displacement with fixed-axis components, combine compatible vectors, and use small exact examples to introduce span, independence, basis and real vector spaces.

Definition
Mathematics & logic · InformationClassical propositions and connectives

Classical logic combines truth-valued propositions using defined connectives.

Definition
Mathematics & logicAxioms, deduction and mathematical proof

A mathematical proof derives a conclusion within stated assumptions and rules.

Method
Mathematics & logic · InformationSets, membership and basic operations

A set specifies membership without counting duplicate listings.

Definition
Mathematics & logic · InformationFunctions, domain and codomain

A function assigns exactly one output to each input in its domain.

Definition
Mathematics & logic · InformationMathematical induction

A base case and general successor step establish a predicate on all nonnegative integers.

Method
Mathematics & logic · MeasurementEuclidean right triangles and the Pythagorean theorem

In a Euclidean right triangle, squared leg lengths sum to the squared hypotenuse length.

Mathematical statement
Mathematics & logic · PhysicsSine, cosine and the unit circle

Sine and cosine are unit-circle coordinates whose squared values sum to one.

Mathematical statement
Mathematics & logic · InformationComplex numbers

A complex number has real coordinates a and b and an imaginary unit satisfying i²=−1.

Definition
Mathematics & logic · Information · PhysicsLinear maps and matrix representation

A linear map preserves linear combinations and has a matrix once bases are chosen.

Definition
Mathematics & logicLimit of a real function

A finite limit controls output error through sufficiently small input distance.

Definition
Mathematics & logic · PhysicsDerivative at a point

A derivative is a finite limit of local difference quotients.

Definition
Mathematics & logic · PhysicsDefinite integral and signed accumulation

A definite integral is the limiting signed accumulation of small contributions.

Definition
DefinitionSource checked

Vectors

Mathematics & logicPhysics

Describe displacement with fixed-axis components, combine compatible vectors, and use small exact examples to introduce span, independence, basis and real vector spaces.

Key knowledge

A planar Euclidean vector can be represented by ordered components in a chosen basis. Vector addition adds corresponding components, and scalar multiplication multiplies every component by the scalar.

Values and equations

u + v = (uₓ + vₓ, uᵧ + vᵧ); λv = (λvₓ, λvᵧ)

u, v
Planar vectors in a common basis
λ
Real scalar

|v| = √(vₓ² + vᵧ²)

vₓ, vᵧ
Components in an orthonormal Cartesian basis
|v|
Euclidean magnitude

Conditions and scope

  • Use the same basis for component operations.
  • In an orthonormal Cartesian basis the magnitude is √(vₓ² + vᵧ²); this formula does not apply unchanged to a nonorthonormal basis.
  • Physical vectors being added must have compatible units.
Sources · 8

References

Sources retain their recorded scope. A source link alone does not establish verification of every statement.

  1. OpenStax University Physics Volume 1 — Vectors and componentsWilliam Moebs, Samuel J. Ling and Jeff Sanny — OpenStax / Rice UniversityTextbook chapterUniversity Physics Volume 1, 2.1 Scalars and VectorsUniversity Physics Volume 1, 2.2 Coordinate Systems and Components of a Vectoropenstax.org
  2. Bureau International des Poids et Mesures (BIPM)2 sources
    1. International vocabulary of metrology, 1.2 Kind of quantityJoint Committee for Guides in Metrology, Working Group 2 — official BIPM-hosted VIM3Reference guidejcgm.bipm.orgRead source
    2. SI Brochure, ninth edition, version 4.01 (2026)Bureau International des Poids et MesuresReference guide · PDFbipm.orgRead source
  3. Mathematics Course 111: Algebra I, Part IV: Vector Spaces (1996–97)D. R. Wilkins — School of Mathematics, Trinity College Dublin, IrelandCourse notes · PDFmaths.tcd.ieRead source
  4. Precalculus 2e, 8.8: VectorsOpenStaxTextbook chapteropenstax.orgRead source
  5. 18.06 Linear Algebra, Lecture 30: Linear transformations and their matrices (transcript)Gilbert Strang / MIT OpenCourseWareCourse notes · PDFocw.mit.eduRead source
  6. MAM1000W Calculus notesJonathan Shock, University of Cape TownTeaching resourceopen.uct.ac.zaRead source

Evidence and review

Two-dimensional Cartesian vector operations and norm.

2026-10-10 · Checked component formulas; scope excludes general abstract vector spaces and curved-space transport.

Foundational review

2026-10-10 · Fresh primary-source inspection of the complete compact record, including every statement, equation, quantity and material condition, followed by independent AI editorial review. This check does not certify all linked lessons or every passage of every cited publication.

Sources from other places

Scope or convention differs

Cartesian components add and scale componentwise, with the Pythagorean norm.

The source uses standard axes; repository basis and compatible-unit conditions prevent overgeneralising its norm formula.

  • University of Cape Town, Department of Mathematics and Applied Mathematics

Related articles

Vectors and vector spaces ↗
Entry detailsPermanent link to this entry ↗
Record identity
vectors
Revision
reference-core.1
Published lesson seed
vectors-spaces