2cos315=2cos(270+45)=2sin45=2*(√2/2)=√2
sin210=sin(180+30)=-sin30=-√3/2
tg420=tg(360+60)=tg60=√3
2cos315+sin210+tg420=√2-√3/2+√3
3cos5/(sin(90-55)+cos65)=3 cos5/(cos55+cos65)=3cos5/2cos60cos5=3/(2*1/2)=3
Cosacosb=1/2(cos(a-b)+cos(a+b))
cos(x+π/3)*cos(x-π/3)-0,25=0
1/2(cos2π/3+cos2x)=0
1/2(-1/2-1/2cos2x-0,25=0
-0,25-0,5cos2x-0,25=0
-1-0,25cos2x=0
cos2x=-4<-1
нет решения