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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

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Live result
Ready
°
Acute
Complement 90−θ 45.0° Supplement 180−θ 135.0° Slope 1.00 · 100% sin·cos·tan 0.707 · 0.707 · 1.000
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Live relations from measured θ

θ (interior)
—
Complement
—
90° − θ
Supplement
—
180° − θ
Reflex & Radians
—
—

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

θ 90−θ 180−θ

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.

Two-line finder → Degrees↔Radians →

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.