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Ответ:

a)

[tex]\left \{ {{y=x-2} \atop {3x+y=2}} \right. \\3x+(x-2)=2\\3x+x-2=2\\4x=4\\x=1\\y=x-2=1-2=-1[/tex]

б)

[tex]\left \{ {{x+5y=15} \atop {2x-y=8}} \right. \\\left \{ {{x+5y=15} \atop {y=2x-8}} \right.\\x+5(2x-8)=15\\x+10x-40=15\\11x=55\\x = 5\\y = 2x-8 = 2*5-8 = 10-8 = 2[/tex]