Rozwiąż układ równań dla y+x=20 i x=20-y

Rozwiązanie zadanego układu równań metodą podstawiania:

$\begin{cases}y+x=20 \\ x=20-y \end{cases}$

$x+y=20x+y=20 $
$ $
$ $
$varc=document.getElementById("myCanvas"); $
$varctx=c.getContext("2d"); $
$ctx.font="18pxArial"; $
$ctx.strokeStyle="#202020";ctx.strokeStyle="#b22222";ctx.strokeText("x",5,24);ctx.font="12pxArial"; $
$ctx.moveTo(35,24);ctx.lineTo(370,24);ctx.stroke(); $
$ctx.strokeStyle="#202020";ctx.strokeText("17",5,48);ctx.moveTo(35,48);ctx.lineTo(370,48);ctx.stroke(); $
$ctx.strokeText("16",5,72);ctx.moveTo(35,72);ctx.lineTo(370,72);ctx.stroke(); $
$ctx.strokeText("15",5,96);ctx.moveTo(35,96);ctx.lineTo(370,96);ctx.stroke(); $
$ctx.strokeText("14",5,120);ctx.moveTo(35,120);ctx.lineTo(370,120);ctx.stroke(); $
$ctx.strokeText("13",5,144);ctx.moveTo(35,144);ctx.lineTo(370,144);ctx.stroke(); $
$ctx.strokeText("12",5,168);ctx.moveTo(35,168);ctx.lineTo(370,168);ctx.stroke(); $
$ctx.strokeText("11",5,192);ctx.moveTo(35,192);ctx.lineTo(370,192);ctx.stroke(); $
$ctx.strokeText("10",5,216);ctx.moveTo(35,216);ctx.lineTo(370,216);ctx.stroke(); $
$ctx.strokeText("9",5,240);ctx.moveTo(35,240);ctx.lineTo(370,240);ctx.stroke(); $
$ctx.strokeText("8",5,264);ctx.moveTo(35,264);ctx.lineTo(370,264);ctx.stroke(); $
$ctx.strokeText("7",5,288);ctx.moveTo(35,288);ctx.lineTo(370,288);ctx.stroke(); $
$ctx.strokeStyle="#202020";ctx.strokeText("1",27,310);ctx.moveTo(35,0);ctx.lineTo(35,290);ctx.strokeStyle='#eee9e9';ctx.stroke(); $
$ctx.strokeStyle="#202020";ctx.strokeText("2",51,310);ctx.moveTo(59,0);ctx.lineTo(59,290);ctx.strokeStyle='#eee9e9';ctx.stroke(); $
$ctx.strokeStyle="#202020";ctx.strokeText("3",75,310);ctx.moveTo(83,0);ctx.lineTo(83,290);ctx.strokeStyle='#eee9e9';ctx.stroke(); $
$ctx.strokeStyle="#202020";ctx.strokeText("4",99,310);ctx.moveTo(107,0);ctx.lineTo(107,290);ctx.strokeStyle='#eee9e9';ctx.stroke(); $
$ctx.strokeStyle="#202020";ctx.strokeText("5",123,310);ctx.moveTo(131,0);ctx.lineTo(131,290);ctx.strokeStyle='#eee9e9';ctx.stroke(); $
$ctx.strokeStyle="#202020";ctx.strokeText("6",147,310);ctx.moveTo(155,0);ctx.lineTo(155,290);ctx.strokeStyle='#eee9e9';ctx.stroke(); $
$ctx.strokeStyle="#202020";ctx.strokeText("7",171,310);ctx.moveTo(179,0);ctx.lineTo(179,290);ctx.strokeStyle='#eee9e9';ctx.stroke(); $
$ctx.strokeStyle="#202020";ctx.strokeText("8",195,310);ctx.moveTo(203,0);ctx.lineTo(203,290);ctx.strokeStyle='#eee9e9';ctx.stroke(); $
$ctx.strokeStyle="#202020";ctx.strokeText("9",219,310);ctx.moveTo(227,0);ctx.lineTo(227,290);ctx.strokeStyle='#eee9e9';ctx.stroke(); $
$ctx.strokeStyle="#202020";ctx.strokeText("10",243,310);ctx.moveTo(251,0);ctx.lineTo(251,290);ctx.strokeStyle='#eee9e9';ctx.stroke(); $
$ctx.strokeStyle="#202020";ctx.strokeText("11",267,310);ctx.moveTo(275,0);ctx.lineTo(275,290);ctx.strokeStyle='#eee9e9';ctx.stroke(); $
$ctx.strokeStyle="#202020";ctx.strokeText("12",291,310);ctx.moveTo(299,0);ctx.lineTo(299,290);ctx.strokeStyle='#eee9e9';ctx.stroke(); $
$ctx.strokeStyle="#202020";ctx.strokeText("13",315,310);ctx.moveTo(323,0);ctx.lineTo(323,290);ctx.strokeStyle='#eee9e9';ctx.stroke(); $
$ctx.strokeStyle="#202020";ctx.strokeText("14",339,310);ctx.moveTo(347,0);ctx.lineTo(347,290);ctx.strokeStyle='#eee9e9';ctx.stroke(); $
$ctx.beginPath();ctx.moveTo(35,0);ctx.lineTo(320,288);ctx.lineWidth=3;ctx.strokeStyle="#ff3399";ctx.stroke(); $
$ctx.beginPath();ctx.moveTo(35,0);ctx.lineTo(106,72);ctx.lineWidth=3;ctx.strokeStyle="#00fa9a";ctx.stroke(); $
$ctx.beginPath();ctx.moveTo(177,144);ctx.lineTo(248,216);ctx.lineWidth=3;ctx.strokeStyle="#00fa9a";ctx.stroke(); $

i: Ostateczne rozwiązanie to:

podany układ ma nieskończenie wiele rozwiązań

  y + (-y +20) = 20
  0 = 0 => x \in {R}