[tex]\it a)\ sin28^o=sin(180^o-28^o)=sin152^o \Rightarrow Expresia\ \ devine:\\ \\ sin^2152^o+cos^2152^o=1\\ \\ \\ b)\ sin15^o=sin(180^o-15^o)=sin165^o \Rightarrow Expresia\ \ devine:\\ \\ cos^2 165^o+sin^2 165^o=1\\ \\ \\ c)\ sin75^o=sin(180^o-75^o)=sin105^o \Rightarrow Expresia\ \ devine:\\ \\ sin105^o-sin105^o=0[/tex]
[tex]\it d)\ cos149^o=-cos(180^o-149^o)=-cos31^o \Rightarrow Expresia\ \ devine:\\ \\ cos31^o-cos31^o=0[/tex]
