If cos-1 x - cos-1 y/2 = alpha, then 4x2 - 4xy cos alpha + y2 = ? (a) 4 (b) 2sin2 alpha (c) -4sin2 alpha (d) 4sin2 alpha Share with your friends Share 15 Manbar Singh answered this We have, cos-1x - cos-1y2 = α⇒cos-1xy2 + 1-x21-y24 = α⇒xy2 + 1-x21-y24 = cos α⇒xy2 + 4-y2-4x2+x2y22 = cos α⇒xy + 4-y2-4x2+x2y22 = cos α⇒xy + 4-y2-4x2+x2y2 = 2 cos α⇒ 4-y2-4x2+x2y2 = 2 cos α - xy⇒4-y2-4x2+x2y2 = 4 cos2α + x2y2 - 4xy cos α⇒4-y2-4x2 = 4 cos2α - 4 xy cos α⇒4x2 + y2 - 4xy cos α = 4 - 4 cos2α⇒4x2 + y2 - 4xy cos α = 41-cos2α⇒4x2 + y2 - 4xy cos α = 4 sin2α 61 View Full Answer
