arcsin1/2=π/6
3/π arcsin1/2=3/π * arcsin1/2=3/π *π/6=1/2
cos2x=1/2
2x=(-1)^n *arcsin1/2+πn,
2x=(-1)^n *π/6+πn,
x=(-1)^n*π/12+πn/2, n∈Z
n=0, x=π/12
n=1, x=-π/12+π/2=5π/12
............................................
n=-1, x=-π/12-π/2=-7π/12,
Наименьшее положительное х=π/12