138
ա sin2a/sina=2sina*cosa=2cosa
բ sin2a/2cos^2a=2sina*cosa/2cos^2a=sina/cosa= tga
գ sin2a/sina-cosa=2cosa-cosa=cosa
դ cos2a-cos^2a=cos^2a-sin^2a-cos^2a=-sin^2a
ե sin^2a+cos2a=sin^2a+cos^2a-sin^2a= cos^2a
զ sin^2a-cos^2a=-cos^2a +sin^2a=-cos2a