-5y2=1.8 y2=1.8:-5 y=

-5*у*2=1,8 у*2=1,8:(-5) у*2=-0,36 у=-0,36:2 у=-0,18                  проверка    -5*(-0,18)*2=1,8                                                       0,9*2=1,8                                                          1,8=1,8