SAT and ACT math terms · SAT Math, ACT Math
Radian
Radian: A unit of angle measure where one radian is the angle that cuts off an arc equal in length to the radius; 2π radians equal 360°.
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What it means
To convert degrees to radians, multiply by π/180; to convert radians to degrees, multiply by 180/π. Arc length in radians is simply s = rθ.
Common values: 90° = π/2, 180° = π, 270° = 3π/2.
Example
An arc with central angle π/3 radians in a circle of radius 6 has length 6 × π/3 = 2π.
On the exam
Radians appear in SAT circle questions and in ACT trigonometry and unit circle questions.