Cos^2a-sin^2a

1-2sin a cos a

1)

(sina-cosa)^2+sin2a=(sin а) ^2 + (cos а) ^2 - 2sin a·cos a + sin 2a =

= 1 - sin 2a + sin 2a = 1

так как (sin a - cos a)^2 = (sin а) ^2 - 2sin a·cos a + (cos а) ^2

(sin а) ^2 + (cos а) ^2=1

sin 2а = 2sin a·cos a

2)

1-4sin^2a*cos^2a= 1-4·[((1-сos 2а) /2)·((1+сos 2а) /2)] = 1 - (1-(cos 2а) ^2) = 1 - (sin 2а) ^2 =

= (cos 2а) ^2

ответ: (cos 2а) ^2