Radian

Radian is the measure of an angle whose vertex is the centre of the circumference and it makes an arc with the same length as the radius
π rad = 180^o

  Exercise: change the radians into degrees or viceversa:

  a) 34^o 15' 17''

  b) 135^o

  c) 3π/2

  d) 5π/3

  Solutions:  a) 0,597 rad; b) 3π/4 rad; c) 270^o; d) 300^o