`9sin^2 2x-6sin2x+1=0`
`<=>(3sin2x-1)^2=0`
`<=> 3sin2x-1=0`
`<=> 3sin2x=1`
`<=> sin2x=1/3`
`<=> [{:(2 x = arcsin (1/3) + k 2 pi ),(2 x = pi - arcsin (1/3) + k 2 pi ):}:}\ ( k \ in \ ZZ )`
`<=> [{:( x = 1/2arcsin (1/3) + kpi ),( x = pi/2 - 1/2arcsin (1/3) + kpi ):}:}\ ( k \ in \ ZZ )`
Vậy `bbS={1/2arcsin (1/3) + kpi; pi/2 - 1/2arcsin (1/3) + kpi | k in ZZ}`