Odpowiedź:
[tex]\left \{ {{x+y+z=10} \atop {x+y-z=20}} \right. \\\left \{ {{x+y+z=10} \atop {x-y-z=30}} \right.\\2x+2y=30\\x=20\\2x+2y=30\\x=20\\y=-5\\x=20\\20-5+z=10\\z=-5\\(x,y,z)=(20,-5,-5)\\\left \{ {{20+(-5)+(-5)=10} \atop {20+(-5)-(-5)=20}} \\\left \{ {{20-(-5)-(-5)=30}\\\\10=10\\20=20\\30=30\\(x,y,z)=(20,-5,-5)\\[/tex]
Szczegółowe wyjaśnienie:
