#-12x-23y=color(red)(17)" (1)"#
#13x+13y=-17 " (2)"#
#color(green)(-1)(13x+13y)=color(green)(-1)(-17)" (2)" #
#-13x-13y=color(red)(17)" (3)"#
#"the equation (1) =the equation (3)"#
#-12x-23y=-13x-13y#
#-12x+13x=-13y+23y#
#color(blue)(x=10y)#
#"now use the equation (1)"#
#-12(color(blue)(10y))-23y=17#
#-120y-23y=17#
#-143y=17#
#y=-17/143#
#y=-0,12#
#"now use the equation (2)"#
#13x+13(-17/143)=-17#
#13x-221/143=-17#
#13x=221/143-17" "13x=1210/143" "x=1210/(13*143)#
#x=0,65#