Rozwiąż układ równań stosując metodę podstawiania: 2)  1/2[latex]/left{ {{1/2x + 2y=8} atop {x/y = 4}} ight.[/latex]   3) x =2y     2x+5y=90   4) x=3y     x+5=2(y+5)   5) x+y=13     10y+x=9+10x+y   6) 2a+2b=34      a-3=b+2

2) 1/2x+2y=8 x/y=4  /·y   1/2x+2y = 8 x = 4y   1/2·4y+2y = 8 x = 4y   2y+2y = 8 x = 4y   4y = 8  /:4 x = 4y   y = 2 x = 4·2   y = 2 x = 8   3) x =2y 2x+5y=90   x = 2y 2·2y+5y = 90   x = 2y 4y+5y = 90   x = 2y 9y = 90  /:9   x = 2y y = 10   x = 2·10 y = 10   x = 20 y = 10   4) x=3y x+5=2(y+5)   x = 3y x+5 = 2y+10   x = 3y x-2y = 10-5   x = 3y 3y-2y = 5   x = 3y y = 5   x = 3·5 y = 5   x = 15 y = 5   5) x+y=13 10y+x=9+10x+y   x = 13-y 10y-y+x-10x = 9   x = 13-y 9y-9x = 9   x = 13-y 9y-9(13-y) = 9   x = 13-y 9y-117+9y = 9   x = 13-y 9y+9y = 9+117   x = 13-y 18y = 126  :18   x = 13-y y = 7   x = 13-7 y = 7   x = 6 y = 7   6) 2a+2b=34 a-3=b+2   2a+2b = 34 a-b = 2+3   2a+2b = 34 a = 5+b   2(5+b)+2b = 34 a = 5+b   10+2b+2b = 34 a = 5+b   2b+2b = 34-10 a = 5+b   4b = 24  /:4 a = 5+b   b = 6 a = 5+6   b = 6 a = 11