7020-m•3=4080
m•3=7020-4080
m•3=2840
m=2840:3
m=980
k•6-2284=5456
k•6=5456+2284
k•6=7740
k=7740:6
k=2580
n:7+1275=6000
n:7=6000-1275
n:7=4725
n=4725:7
n=675
2160:u+4996=5000
2160:u=5000-4996
2160:u=4
u=2160:4
u=540
5cos(2a)=5(cos^2(a) - sin^2(a))=5(1 - sin^2(a) - sin^2(a))=5(1 -2sin^2(a))
При sina=-0,9
5(1 - 2×(-0,9)^2)=5(1 - 2×0,81)=5(1-1,62)=5×(-0,62)=-3,1