Question

O conjunto solução do sistema a seguir é:
x + y = 12
{
3x - y = 20
A) S= {10, 2}
B) S= {8, 4}
C) S= {2,10}
D) S= {4,8}

Answer 1

$Resuminho..\\\\\begin{bmatrix}x+y=12\\ 3x-y=20\end{bmatrix}\\\\\begin{bmatrix}3\left(12-y\right)-y=20\end{bmatrix}\\\\\begin{bmatrix}36-4y=20\end{bmatrix}\\\\\mathrm{Para\:}x=12-y\\\\\mathrm{Substituir\:}y=4\\\\x=12-4\\\\x=8\\\\x=8,\:y=4$

RESPOSTA > B) S= {8, 4}