Объяснение:
1) cos2a +1 / 2-2sin^2 a =cos^2 a -sin^2 a+cos^2 a +sin^2 a /2(1-sin^2 a) =
2cos^ a / 2cos^2 a=1
2) 2sinacosa / cos^2 a-sin^2 a+sin^2 a+cos^2 a =2sinacosa /2cos^2 a=
sina/cosa =tga
