If cosx = 10/19 an pi < x < 2pi, find the exact value of cos x/2
Use the double angle formula.
Cos 2Y= sin^2 Y - cos^2Y = 1-2Cos^2 Y.
let y= x/2, and 2Y=x
Use the double angle formula.
Cos 2Y= sin^2 Y - cos^2Y = 1-2Cos^2 Y.
let y= x/2, and 2Y=x
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