tan12Sin−12x1+x2−12Cos−11−y21+y2=
2x1−x2
0
x−y1+xy
1
Let x=tanA;y=tanB. Then tan12sin-12x1+x2-12cos-11-x21+x2=tan12sin-12tanA1+tanA2-12cos-11-tanB21+tanB2 =tan12sin-1sin2A-12cos-1cos2B =tanA-B =tanA-tanB1+tanAtanB =x-y1+xy