1)Cos2a/Cosa-Sina= Cos^2-Sin^2/Cosa -Sina= Cosa-Sina3)Sin^2*Ctga/Sin2a=Sin^2* (Cosa/Sina)/2sinacosa=(Sina^2*Cosa/Sina)/2sinacosa=SinaCosa/2sinacosa=1/2
1)Cos2a/Cosa-Sina= Cos^2-Sin^2/Cosa -Sina= Cosa-Sina
3)Sin^2*Ctga/Sin2a=Sin^2* (Cosa/Sina)/2sinacosa=(Sina^2*Cosa/Sina)/2sinacosa=SinaCosa/2sinacosa=1/2