Complex numbers
A complex number has real coordinates a and b and an imaginary unit satisfying i²=−1.
Key knowledge
A complex number is written z=a+bi with real a and b and i²=−1. Its real part is a and its imaginary part is b. It is represented by (a,b) in the complex plane; addition combines the two components and multiplication uses i²=−1.
Values and equations
(a+bi)+(c+di)=(a+c)+(b+d)i; (a+bi)(c+di)=(ac−bd)+(ad+bc)i
- a, b, c, d
- Real coefficients
- i
- Imaginary unit with i²=−1
Conditions and scope
- The imaginary part is the real coefficient b, not the product bi.
- When b=0 the number is real; when a=b=0 it is zero.
The actual selected NCERT chapter inspection is the Math/Information author’s continuation evidence; this editor binds that exact proposal. No new whole-chapter proof or all complex-analysis review is inferred.
Sources · 3
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
- Mathematics, Class 11 (Reprint 2026–27), §§4.2–4.3 and 4.5: Complex numbers, algebra and Argand planeNational Council of Educational Research and Training (NCERT), IndiaTextbook chapter · PDF
- Precalculus 2e, §3.1: Complex-plane representation and component operationsOpenStax, Rice UniversityTextbook chapter
- MAM1000W Calculus notesJonathan Shock, University of Cape TownTeaching resource
Evidence and review
Complex coordinates, equality, addition and multiplication.
The Argand plane is §4.5; §4.4 covers modulus and conjugation. Preserve the valid page-fragment citations. Citation metadata only: complex-number statements, equations, conditions and page-fragment URLs remain unchanged.
2026-10-10 · Compared definitions and operations; retained NCERT's coefficient definition of imaginary part and excluded misleading division restrictions in both textbook discussions.
2026-10-11 · Continuation author/editor source-check scope: The Argand plane is §4.5; §4.4 covers modulus and conjugation. Preserve the valid page-fragment citations. Citation metadata only: complex-number statements, equations, conditions and page-fragment URLs remain unchanged. The actual selected NCERT chapter inspection is the Math/Information author’s continuation evidence; this editor binds that exact proposal. No new whole-chapter proof or all complex-analysis review is inferred. Exact independent adoption review is pending; historical reviews retain their original date and scope.
Foundational review
2026-10-11 · Historical approval retained from its original dated scope: 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. Continuation 2026-10-11: math-complex-numbers: The Argand plane is §4.5; §4.4 covers modulus and conjugation. Preserve the valid page-fragment citations. Citation metadata only: complex-number statements, equations, conditions and page-fragment URLs remain unchanged. Unchanged claim and inventory decisions are carried forward; this delta is not a new whole-field, whole-document or human certification.
Sources from other places
Agreement within this scope
Complex numbers have real components, imaginary coefficient, plane representation and algebra using i squared equals minus one.
The imaginary part is the coefficient, not its product with i. math-complex-numbers: The Argand plane is §4.5; §4.4 covers modulus and conjugation. Preserve the valid page-fragment citations. Citation metadata only: complex-number statements, equations, conditions and page-fragment URLs remain unchanged. The earlier independent complex-number comparison is retained; this delta corrects the NCERT reference locator/edition, not its algebra.
University of Cape Town, Department of Mathematics and Applied Mathematics
- MAM1000W Calculus notes South AfricaEnglish
§10.2, printed pp.96–98 (PDF pp.99–101)
- MAM1000W Calculus notes
Entry details
Permanent link to this entry ↗- Record identity
- math-complex-numbers
- Revision
- core.1.continuation-20261011.1
- Structured reference record
- Essential core · first collection