Cos 180 Degrees

Sin, Cos, Tan, Cot of an Angle
Function
Angle (°)

What is cos 180°?

Answer

cos 180° =
−1

Angle in radians: 180° = π. The point of the angle is on the x-axis: (−1, 0).

P(cos 180°, sin 180°) = (−1, 0)

xyOP

P(cos 180°, sin 180°) = (−1, 0)

Highlighted: the projection on the x-axis — cosine, x = −1.

All four functions of 180°
FunctionExact valueDecimal
sin 180°00
cos 180°−1−1
tan 180°00
cot 180°undefined—

Reference angle: cos 0° = 1

See Also

Recalculate with different values ↑

Cosine of nearby angles

Anglecos
167°≈ −0.9744
175°≈ −0.9962
179°≈ −0.9998
180°−1
195°−(√6 + √2)/4
198°−√(10 + 2√5)/4
200°≈ −0.9397

FAQ

What is cos 180°?

cos 180° = −1

Why is cos 180° equal to −1?

The point of 180° on the unit circle is (−1, 0), and cosine is its the x-coordinate, so cos 180° = −1.

Why does a calculator show −0.5985 for cos 180?

The calculator is in radian mode (RAD): it takes cos 180 as the cosine of 180 radians, cos 180 rad ≈ −0.5985. Switch it to degrees (DEG): cos 180° = −1. In radians the value is never undefined: π is irrational, so a whole number of radians never lands exactly on an axis.

See Also