Obtuse Angle Calculator
Calculate properties of obtuse angles and triangles containing obtuse angles.
Obtuse Angle
120 is an obtuse angle (between 90 and 180)
Triangle with Obtuse Angle
Enter two sides adjacent to the obtuse angle
Angle: 120
Radians
2.0944
Supplementary
60.00
Trigonometric Values
sin(120)0.866025
cos(120)-0.500000
tan(120)-1.732051
Reference Angle60.00
Note: For obtuse angles, cosine is always negative.
Triangle Solution
Side c (opposite to C)10.4403
Angle A24.50
Angle B35.50
Perimeter22.4403
Area15.1554 sq units
Obtuse Angle Information
Angle Classification
Acute: 0° - 90°
Obtuse: 90° - 180°
Reflex: 180° - 360°
Law of Cosines
c = a + b - 2ab*cos(C)
When C is obtuse, cos(C) is negative, so c > a + b would be expected.
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Editorial Note
MyCalcBuddy Editorial Team
This page is maintained as an educational calculator reference.
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Formula Source: Handbook of Mathematical Functions
by Abramowitz & Stegun
🔄Last reviewed: May 2026
✓Formula checks are based on standard references and internal QA review.