A =
11−msin2a +
11−msin2b = 2−msin2b−msin2a(1−msin2a)(1−msin2b
= 2−2msin(a+b)cos(a−b)1+m2sin2asinb−msin2a−msin2b
= 2−2cos2(a−b)1+12m2cos2(a−b)+12m2cos2(a+b)−2msin(a+b)cos(a−b)
= 2−2cos2(a−b)1+12m22cos2(a−b)−12m2+12m2.2sin2(a+b)−12m2−2cos2(a−b)
= 2[1−cos2(a−b)][1−cos2(a−b)]+m2[cos2(a−b)−1]
= 21−m2