What is it
Radians are an alternative way of measuring angles based on the radius of a circle, where 2π radians equals 360° — used throughout A-Level calculus because they make trigonometric derivatives and integrals dramatically simpler.
Why it matters
Calculus with trigonometric functions only works cleanly in radians — using degrees would make the derivative of sin(x) an ugly, impractical expression, so this seemingly small change in units underpins a huge amount of later work.
Exam tip
Get comfortable converting between degrees and radians in both directions before tackling calculus questions — a wrong units assumption here silently invalidates an otherwise correct calculus answer.
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