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}