Evaluate sin(1/2 cos^-1 4/5)

• 1/sqrt10
  put cos^-1 4/5=a
  cosa=4/5 so sina=3/5
  now sina=2sina/2cosa/2
  3/5=2sina/2sqrt((1+cosa)/2)
  such that sina/2=1/sqrt10
• 11 years agoHelpfull: Yes(1) No(0)
• using Pythagoras triplets (3,4,5) the smallest angle is 37 degree.
  so cos^-1 (4/5)= 37degree
  sin(1/2 cos^-1 (4/5))
  = sin(37/2)
  = sin(18.5)= 0.317=1/sqrt10
• 11 years agoHelpfull: Yes(1) No(1)