5cos57/sin33
cos меняем на sin (90-57)=sin33
5sin33/sin33 = 5
3/ tg(a+b)=(tga+tgb)/(1-tgatgb)=(2+1)/(1-2*1)=3/-1=-3
1/ cos70cos10+sin70sin10=cos60
sin50cos10+cos50sin10=sin60
cos60/sin60=ctg60=√3/3
cos(105)=cos(60+45)=cos60cos45-sin60sin45=1/2*√2/2-√2/2*√3/2=√2/4(1-√3)