Radian Measure (Edexcel IGCSE Further Pure Maths)

Radian Measure

What are radians?

• Radians are an alternative to degrees for measuring angles

• 1 radian is defined as the angle in a circle sector of radius 1 and arc length 1

• Radians are often given in terms of

  •  radians = 360°

  • radians = 180°

• The symbol for radians is ^c but it is more usual to see rad

  • When is involved, no symbol for radians is needed

    • With it is obvious it is in radians

  • You should never omit the symbol for degrees

• In the exam a question will usually tell you which angle measure to use

  • But radians must be used if calculus with the trigonometric functions is involved

How do I convert between radians and degrees?

• Use radians = 180° to convert between radians and degrees

  • To convert from radians to degrees multiply by 

  • To convert from degrees to radians multiply by 

• Some of the common equivalents are:

  • 

  • 

  • 

  • 

  • 

  • 

• It is useful to remember these and use them to work out other conversions

• Your calculator will be able to work with both radians and degrees