a)1-sin^2a=sin^2a+cos^2a-sin^2a=cos^2a
б)1-c0s^2a=sin^2a
b)sin^2a-1=sin^a-cos^2a-sin^2a=-cos^2a
г)cos^2a=1-sin^2a
a)(1+sina)(1-sina)=1-sin^2a
б)(cosa-1)(1+cosa)=cos^2a-1
b)cos^2a-sin^2a+1=cos^2a-sin^2a+cos^2a+sin^2a=2cos^2a
г)1+sin^2a-cos^2a=cos^2a+sin^2a+sin^2a-cos^2a=2sin^2a
a)1-sin^2a-cos^2a=cos^2a-cos^2a=0
sin^4a-cos^4a=(sin^2a-cos^2a)(sin^2a+cos^2a)=sin^2a-cos^2a=-(cos^2a-sin^2a)=-cos2a
b)sin^4a-cos^4a-(cos^2a-sin^2a)=-cos2a-cos2a=-2cos2a
г)(sina+cosa)^2+(sina-cosa)^2=1+2sinacosa+1-2sinacosa=2
