5*sina=8*sin(a/2); 5*2*sin(a/2)*cos(a/2)=8*sina(a/2) 5*cos(a/2)=4 cos(a/2)=4/5 cos(a/2)=√((1+cos(a))/2) cosa=2*(cos(a/2)^2)-1 cosa=(4/5)^2*2-1 cosa=7/25cosa=√((1+cos2a)/2) cos2a=2*(cos(a2)^2)-1 cos2...