Объяснение:
a) sin70° · cos250° < 0
sin70° > 0
cos250°=cos(180°+70°)= -cos70° < 0
б) tg π/5 · ctg 4π/3 > 0
tg π/5 > 0
ctg 4π/3 =ctg(π+π/3)=ctg π/3 >0
в) sin 9π/7 · cos π/5 · tg 7π/3 < 0
sin 9π/7=sin(π + 2π/7)= -sin 2π/7 < 0
cos π/5 > 0
tg 7π/3=tg (2π + π/3)=tg π/3 >0
