urgent ..
formula for sin-1X + sin-1Y , sin-1X -sin-1Y
cos-1X + cos-1Y
cos-1X - cos-1Y
sin - 1 x + sin-1 y = sin -1 (x√1-y2 + y√1-x2)
sin-1x- sin-1y = sin-1(x√1-y2 -y√1-x2)
cos-1x + cos-1y = cos-1[xy - √(1-y2)(1-x2)]
cos-1x - cos-1y = cos-1[xy + √(1-y2)(1-x2)]