#sin (5x) cos (7x) — cos (5x) sin (7x) =-0.55#
#sin(5x-7x)=-0.55#—>#sin (A-B)=sinAcosB-cosAsinB#
#sin(-2x)=-0.55#
#-sin(2x)=-0.55#—>#sin(-x)=-sin x#
#sin(2x)=0.55#
#2x=sin^-1 0.55#
#2x=0.5823642379+2pin or 2x=2.559228416 +2pin#
#x=0.2911821189+pin or x=1.279614208+pin#—>divide by 2
#n=0, x=0.29, 1.28#
#S={0.29}#