12.1

1) 1 - cos2a = sin2a

2)sin2b - 1 = sin2b - sin2b-cos2b = -cos2b

3)sin2ф + cos2a + 1 = 1+1 = 2

4)1/cos2a - 1 = (1-cos2a)/cos2a = tg2a

5) 1 - sin2a + sin2a/tg2a = cos2a + sin2a*cos2a/sin2a = 2cos2a

6)(sina + cosa)2 + (sina - cosa)2 = sin2a + 2sina*cosa + cos2a + sin2a - 2sina*cosa + cos2a = 2sin2a + 2cos2a = 2*1 = 2