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Д) x-y=12     (4-y)-y=12    16-8y+y-y=12      16-8y=12

                      :                        :                              :                      :

     x+y=4        x=4-y               x=4-y                     x=4-y

      -8y=12-16     -8y=-4       8y=4       y=0.5        y=0.5

                          :                :                :                  :

      x=4-y            x=4-y         x=4-y     x=4-0.5     x=3.5

ответ:(3.5;0.5)

Ё)4x-y=1      4x-y=1     4x-(-1-2x)=1      4x-1+4x-4x=1

                      :                  :                            :                              :

    2x+y=-1      y=-1-2x      y=-1-2x                y=-1-2x

    -1+4x=1      4x=2        x=0.5       x=0.5

                     :                :                :

   y=-1-2x       y=-1-2x    y=-1-1      y=-2

ответ;(0.5;-2)