Помогите решить примеры:

) sin 107°×sin167°+sin 197°×sin 257°
2)4sin10°×sin30°×sin50°×sin70°
3)7/√3×sin18°×sin54°×sin60°

1sin107*sin167+sin197*sin257=sin(90+17)*sin(180-13)+sin(180+17)*sin(270-13)=cos17*sin13-sin17*(-cos13)=sin13*cos17+sin17cos13=sin(13+17)=sin30=1/224sin10*sin30*sin50*sin70=4sin10*1/2*sin50*sin70=2sin10*sin50*sin70==2*sin10*1/2*(cos(70-50)-cos(70+50))=sin10*(cos20-cos120)==sin10(cos20+1/2)37/√3*√3/2*sin18*sin54=3,5*sin18*sin54=3,5sin18cos36