How do you use a half-angle formula to simplify cos 195? Trigonometry Trigonometric Identities and Equations Half-Angle Identities 1 Answer Nghi N. Jun 6, 2015 Use trig identity 2cos^2a = 1 + cos 2a cos 390 = cos (30 +360) = cos 30 = sqrt3/2 2cos^2 195 = 1 + cos 390 = 1 + 0.866 = 1.866 cos^2 195 = 1.866/2 = 0.93 -> # cos 195 = - 0.97 (Quadrant III) 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 cos15using the half-angle identity? See all questions in Half-Angle Identities Impact of this question 2857 views around the world You can reuse this answer Creative Commons License