Ответ:

1)

    [tex]|-x|=3.5\left \{ {{-x=3.5} \atop {-x=-3.5}} \right. \left \{ {{x=-3.5} \atop {x=3.5}} \right.[/tex]

2)

      [tex]-|x|=1.8\left \{ {{-x=1.8} \atop {x=-1.8}} \right.\left \{ {{x=-1.8} \atop {x=-1.8}} \right.[/tex]