How do you use half angle formula to find #sin 22.5#? Trigonometry Trigonometric Identities and Equations Half-Angle Identities 1 Answer Nghi N. May 16, 2015 Trig identity: #2sin^a = 1 - cos 2a# #2(sin 22.5)^2 = 1 - cos 45 # = 1 - (sqr2)/2 = 0.293 #sin^2 (22.5) = 0.146 -> sin (22.5) = 0.38# Answer link Related questions What is the Half-Angle Identities? How do you use the half angle identity to find cos 105? How do you use the half angle identity to find cos 15? How do you use the half angle identity to find sin 105? How do you use the half angle identity to find #tan (pi/8)#? How do you use half angle identities to solve equations? How do you solve #\sin^2 \theta = 2 \sin^2 \frac{\theta}{2} # over the interval #[0,2pi]#? How do you find the exact value for #sin105# using the half‐angle identity? How do you find the exact value for #cos165# using the half‐angle identity? How do you find the exact value of #cos15#using the half-angle identity? See all questions in Half-Angle Identities Impact of this question 3185 views around the world You can reuse this answer Creative Commons License