cos(120°) = -0.5, exactly −1/2.
cos(120°) = -0.5, exactly −1/2. The angle 120° equals 2π/3 radians (120 × π/180).
Exact form: −1/2. Decimal: -0.5 (rounded to 8 places).
120° lies quadrant II. Remember that cosine is positive in quadrants I and IV, and negative in the others, which decides the sign of the answer.
If you get a different number, the calculator is probably in RAD mode. In radians you would enter 2π/3 instead of 120.
| sin 120° | = 0.8660254 |
| cos 120° | = -0.5 |
| tan 120° | = -1.73205081 |
| Angle | Radians | Cos |
|---|---|---|
| 0° | 0 | 1 |
| 30° | π/6 | 0.866025 |
| 45° | π/4 | 0.707107 |
| 60° | π/3 | 0.5 |
| 90° | π/2 | 0 |
| 120° | 2π/3 | -0.5 |
| 135° | 3π/4 | -0.707107 |
| 150° | 5π/6 | -0.866025 |
| 180° | π | -1 |
| 270° | 3π/2 | 0 |
| 360° | 2π | 1 |
cos(120°) = -0.5, exactly −1/2.
120° = 2π/3 radians, so cos(120°) = cos(2π/3) = -0.5.
It is most likely set to radians. Switch to degree (DEG) mode before entering the angle.
Negative.
Yes. Use the calculator on this page, or open the full free Scientific Calculator with memory, history and keyboard support.