Rozwiąż układ równań dla x+y=70 i x+4=y-3

Rozwiązanie zadanego układu równań metodą podstawiania:

$\begin{cases}x+y=70 \\ x+4=y-3 \end{cases}$

$y+x=70y+x=-7 $
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$varctx=c.getContext("2d"); $
$ctx.font="18pxArial"; $
$ctx.strokeStyle="#202020";ctx.strokeStyle="#b22222";ctx.strokeText("y",7,24);ctx.font="12pxArial"; $
$ctx.moveTo(27,24);ctx.lineTo(291,24);ctx.stroke(); $
$ctx.strokeStyle="#202020";ctx.strokeText("42",7,48);ctx.moveTo(27,48);ctx.lineTo(291,48);ctx.stroke(); $
$ctx.strokeText("41",7,72);ctx.moveTo(27,72);ctx.lineTo(291,72);ctx.stroke(); $
$ctx.strokeText("40",7,96);ctx.moveTo(27,96);ctx.lineTo(291,96);ctx.stroke(); $
$ctx.strokeText("39",7,120);ctx.moveTo(27,120);ctx.lineTo(291,120);ctx.stroke(); $
$ctx.strokeText("38",7,144);ctx.moveTo(27,144);ctx.lineTo(291,144);ctx.stroke(); $
$ctx.strokeText("37",7,168);ctx.moveTo(27,168);ctx.lineTo(291,168);ctx.stroke(); $
$ctx.strokeText("36",7,192);ctx.moveTo(27,192);ctx.lineTo(291,192);ctx.stroke(); $
$ctx.strokeText("35",7,216);ctx.moveTo(27,216);ctx.lineTo(291,216);ctx.stroke(); $
$ctx.strokeText("34",7,240);ctx.moveTo(27,240);ctx.lineTo(291,240);ctx.stroke(); $
$ctx.strokeText("33",7,264);ctx.moveTo(27,264);ctx.lineTo(291,264);ctx.stroke(); $
$ctx.strokeText("32",7,288);ctx.moveTo(27,288);ctx.lineTo(291,288);ctx.stroke(); $
$ctx.strokeStyle="#202020";ctx.strokeText("25",19,310);ctx.moveTo(27,0);ctx.lineTo(27,290);ctx.strokeStyle='#eee9e9';ctx.stroke(); $
$ctx.strokeStyle="#202020";ctx.strokeText("26",43,310);ctx.moveTo(51,0);ctx.lineTo(51,290);ctx.strokeStyle='#eee9e9';ctx.stroke(); $
$ctx.strokeStyle="#202020";ctx.strokeText("27",67,310);ctx.moveTo(75,0);ctx.lineTo(75,290);ctx.strokeStyle='#eee9e9';ctx.stroke(); $
$ctx.strokeStyle="#202020";ctx.strokeText("28",91,310);ctx.moveTo(99,0);ctx.lineTo(99,290);ctx.strokeStyle='#eee9e9';ctx.stroke(); $
$ctx.strokeStyle="#202020";ctx.strokeText("29",115,310);ctx.moveTo(123,0);ctx.lineTo(123,290);ctx.strokeStyle='#eee9e9';ctx.stroke(); $
$ctx.strokeStyle="#202020";ctx.strokeText("30",139,310);ctx.moveTo(147,0);ctx.lineTo(147,290);ctx.strokeStyle='#eee9e9';ctx.stroke(); $
$ctx.strokeStyle="#202020";ctx.strokeText("31",163,310);ctx.moveTo(171,0);ctx.lineTo(171,290);ctx.strokeStyle='#eee9e9';ctx.stroke(); $
$ctx.strokeStyle="#202020";ctx.strokeText("32",187,310);ctx.moveTo(195,0);ctx.lineTo(195,290);ctx.strokeStyle='#eee9e9';ctx.stroke(); $
$ctx.strokeStyle="#202020";ctx.strokeText("33",211,310);ctx.moveTo(219,0);ctx.lineTo(219,290);ctx.strokeStyle='#eee9e9';ctx.stroke(); $
$ctx.strokeStyle="#202020";ctx.strokeText("34",235,310);ctx.moveTo(243,0);ctx.lineTo(243,290);ctx.strokeStyle='#eee9e9';ctx.stroke(); $
$ctx.strokeStyle="#202020";ctx.strokeStyle="#b22222";ctx.font="18pxArial"; $
$ctx.strokeText("x",259,310);ctx.font="11pxArial"; $
$ctx.moveTo(267,0);ctx.lineTo(267,290);ctx.strokeStyle='#eee9e9';ctx.stroke(); $
$ctx.beginPath();ctx.moveTo(289,240);ctx.lineTo(50,0);ctx.lineWidth=3;ctx.strokeStyle="#ff3399";ctx.stroke(); $
$ctx.beginPath();ctx.moveTo(289,24);ctx.lineTo(27,288);ctx.lineWidth=3;ctx.strokeStyle="#006633";ctx.stroke(); $

i: Ostateczne rozwiązanie to:

x = y - 7

  (y -7) + y = 70
  2y = 77
  2y = 77 

  y = 77/2 
  x = y-7
  y = 77/2  x = (77/2)-7 = 63/2 
 {x,y} = {63/2,77/2}