-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