Sine, cosine and the unit circle
Sine and cosine are unit-circle coordinates whose squared values sum to one.
Key knowledge
For a real angle θ, the point reached on the unit circle has coordinates (cos θ, sin θ). Therefore cos²θ+sin²θ=1 for every real θ.
Values and equations
(x,y) = (cos θ, sin θ); cos²θ + sin²θ = 1
- θ
- Real angle measured from the positive x-axis rad
- x, y
- Coordinates on the unit circle dimensionless
Conditions and scope
- Use one angle convention consistently; θ is in radians in the displayed coordinate definition.
- A squared value does not determine its sign; the angle's quadrant matters.
Sources · 3
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
- Precalculus 2e, 5.2: Unit-circle sine and cosineOpenStaxTextbook chapter
- Mathematics, Class 10, §8.4: Trigonometric identities on 0°–90°National Council of Educational Research and Training (NCERT), IndiaTextbook chapter · PDF
- TIMES · Further trigonometryAMSI and University of Melbourne, ICE-EMTeaching resource
Evidence and review
Real-angle unit-circle definitions and sine-cosine identity.
2026-10-10 · Compared the all-real unit-circle identity with NCERT's explicitly limited right-triangle angle domain; no new proof object is claimed.
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
Unit-circle sine/cosine coordinates and their squared identity.
The inspected module concentrates on 0–180 degrees; the repository all-real-angle convention is broader.
Australian Mathematical Sciences Institute and University of Melbourne
- TIMES · Further trigonometry AustraliaEnglish
Dealing with obtuse angles; Trigonometric identities
- TIMES · Further trigonometry
Entry details
Permanent link to this entry ↗- Record identity
- math-sine-cosine
- Revision
- core.1
- Structured reference record
- Essential core · first collection