Question
If cos-1x - cos-1(y/2) = α , then 4x2-4xycosα + y2 is equal to ?
Joshi sir comment
according to the given condition
cos-1x = cos-1(y/2) + a
so x = cos ( cos-1y/2 + a)
so x = y/2 cosa - sin cos-1y/2 + sina
so x = y/2 cosa - [1-(y2/4)]1/2 + sina
so x - sina - y/2 cosa = -[1-(y2/4)]1/2
now square both side and solve