Oblicz układ równań metodą podstawiania a) 1/2x+y=4 2x-4y=8 b) 3x-2=2y y-6x=-5/2 c) 1/2x-1/2y=-4 -2+1/3y=8

a) [latex] left { {{ frac{1}{2}x+y =4} atop {2x-4y=8}} ight. [/latex] [latex] left { {{x=8-2y} atop {2x-4y=8}} ight. [/latex] [latex] left { {{x=8-2y} atop {2(8-2y)-4y=8}} ight. [/latex] [latex] left { {{x=8-2y} atop {16-4y-4y=8}} ight. [/latex] [latex] left { {{x=8-2y} atop {-8y=-8}} ight. [/latex] [latex] left { {{x=8-2y} atop {y=1}} ight. [/latex] [latex] left { {{x=8-2*1} atop {y=1}} ight. [/latex] [latex] left { {{x=6} atop {y=1}} ight. [/latex]