cosa = 4\корень из 41
sina = корень(1-(cosa)^2) = 5\корень41
домножим числ. и знамен. на корень из 41
числ. = 4+5=9
знамен. = 2*5-4 = 6
9/6 = 1,5
2cos(x-π/6)=√3
cos(x-π/6)=√3/2
cos(2π-(x-π/6) )=√3/2
x-π/6=arccos(√3/2)
cos(13π/6- x)=√3/2
x- π/6=π/6
13π/6 - x=arccos(√3/2)
x- π/6=π/6 + 2kπ, k ∈ z
13π/6 - x = π/6
x= π/3+2πk,kϵz
13π/6 - x=π/6+2πk,kϵz
x=2π-2kπ,kϵz
x=0+2πk,kϵz
x=2πk,kϵz
Смотри....................