Lesson 25- Radian

 Find the circumference of a circle with radius = 1:
C= 2πr                                                                
C= 2π1
C= 2π
C= 6.3cm 
Find half a circle:
C_180®= 2 π  = πr             C₉₀= πr                    C₆₀= πr            C₄₅= πr
              2                                 2                              3                      4
Definition of Radian:
π= 3.14

Degree:	Radian:	Radian: (dec)
360°	2π	6.28
180°	π	3.14                                   -Must know!
90°	π/2	1.57                                   -Must know!
60°	π/3	1.05
45°	π/4	0.79
30°	π/5	0.57

Degrees → Radians   *find cousins
120° →  2π/ 3       150° → 5π/6     135° → 3π/ 4


1 radian → 57.3°  

Formula of Degrees → Radians or Radians→ Degrees
         π =  180
         r          d


C= Ѳr
C: arc length subtended from part circle    r: radius
Ѳ: standard angle( rads)