Cos 100 Degrees

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

What is cos 100°?

Answer

cos 100° ≈
−0.1736

Angle in radians: 100° = 5π/9. The point of the angle is in quadrant II, where cosine is negative.

≈ — rounded to 4 decimal places. cos 100° can't be written with square roots: 100° is not a multiple of 3°.

cos 100° = cos(180° − 80°) = −cos 80° ≈ −0.1736

P(cos 100°, sin 100°) ≈ (−0.1736, 0.9848)

xyOP

P(cos 100°, sin 100°) ≈ (−0.1736, 0.9848)

Highlighted: the projection on the x-axis — cosine, x ≈ −0.1736.

All four functions of 100°
FunctionExact valueDecimal
sin 100°—≈ 0.9848
cos 100°—≈ −0.1736
tan 100°—≈ −5.6713
cot 100°—≈ −0.1763

Reference angle: cos 80° ≈ 0.1736

See Also

Recalculate with different values ↑

Cosine of nearby angles

Anglecos
90°0
97°≈ −0.1219
98°≈ −0.1392
100°≈ −0.1736
101°≈ −0.1908
105°−(√6 − √2)/4
106°≈ −0.2756

FAQ

What is cos 100°?

cos 100° ≈ −0.1736

Why does cos 100° have no exact value?

A trigonometric value of a whole number of degrees can be written with square roots only when the angle is a multiple of 3°. 100° is not, so no such exact form exists; the value is used as a decimal: cos 100° ≈ −0.1736.

Why does a calculator show 0.8623 for cos 100?

The calculator is in radian mode (RAD): it takes cos 100 as the cosine of 100 radians, cos 100 rad ≈ 0.8623. Switch it to degrees (DEG): cos 100° ≈ −0.1736. In radians the value is never undefined: π is irrational, so a whole number of radians never lands exactly on an axis.

See Also