Complement · Supplement · Reflex
Angle Relationships
Measure one angle — see its complement, supplement, reflex and radians live. Place the center on the vertex, align two rays, and the relations update instantly. Original guide, no copy.
Updated Online Protractor
Keyboard: Tab handles, arrows nudge 1px center / 1° ray (Shift 10px / 5°), R reset, G grid, L lock baseline, Z undo, Shift+Z redo, +/- zoom. Endpoint magnifier shows while dragging. Drag center, baseline ray, second ray. Snap preview before commit. Image stays local — never uploaded. Press Esc to exit fullscreen.
Camera stays local — capture is processed in your browser
Live relations from measured θ
Complement only when θ ≤ 90°, supplement when θ ≤ 180°. Reflex always 360° − θ. Formulas are transparent; explain to beginners and let advanced toggle Off/1° snap.
Original diagram
Transparency
Calculation: θ = arccos(dot/|A||B|) → normalize 0–360 → interior ≤180. Relations are arithmetic. No hidden steps. Decimal precision is display only — see accuracy.
FAQ
When is complement valid?
Only when θ ≤ 90°. Complement is 90° − θ, the angle needed to make a right angle. Above 90° we show '—'.
What about radians?
Radians = θ × π/180. Example 60° = π/3 ≈ 1.047 rad. Toggle degrees/radians in the toolbar; the relations below show both.