A) tg75-tg15=sin75/cos75-sin15/cos15=(sin75*cos15-sin15*cos75)/(cos75*cos15)=
sin(90-15)*cos15-sin15*cos(90-15)/(cos(90-15)*cos15)=(cos15*cos15-sin15*sin15)/(sin15*cos15)=(cos^2(15)-sin^2(15))/(sin15*cos15)=cos30/(sin15*cos15)=
корень(3)/(2*sin15*cos15)=корень(3)/sin30=2*корень(3).