Question

Resolva pelo método de adição:

{x+y=20
{3x+4y=72

Answer 1

$\left \{ {{x+y=20} \atop {3x+4y=72}} \right. \\\left \{ {{(x+y)(-3)=20(-3)} \atop {3x+4y=72}} \right. \\\\\frac{\left \{ {{-3x-3y=-60} \atop {3x+4y=72}} \right.}{y=12} \\\\\fbox{y = 12}\\\\x + y = 20\\x + 12 = 20\\x = 20 - 12\\x = 8\\\\\fbox{x = 8}$