Question

Resolva: x+y=6 x-y=8 Com prova real se conseguirem!!

Answer 1

    $\left\{\begin{array}{ll}x+y=6\\x-y=8\end{array}\right\Leftrightarrow$

$\Leftrightarrow\left\{\begin{array}{ll}y=6-x\\x-y=8\end{array}\right\Leftrightarrow$

$\Leftrightarrow\left\{\begin{array}{ll}y=6-x\\x-(6-x)=8\end{array}\right\Leftrightarrow$

$\Leftrightarrow\left\{\begin{array}{ll}y=6-x\\x-6+x=8\end{array}\right\Leftrightarrow$

$\Leftrightarrow\left\{\begin{array}{ll}y=6-x\\x+x=8+6\end{array}\right\Leftrightarrow$

$\Leftrightarrow\left\{\begin{array}{ll}y=6-x\\2x=14\end{array}\right\Leftrightarrow$

$\Leftrightarrow\left\{\begin{array}{ll}y=6-x\\x=\frac{14}{2}\end{array}\right\Leftrightarrow$

$\Leftrightarrow\left\{\begin{array}{ll}y=6-x\\x=7\end{array}\right\Leftrightarrow$

$\Leftrightarrow\left\{\begin{array}{ll}y=6-7\\x=7\end{array}\right\Leftrightarrow$

$\Leftrightarrow\left\{\begin{array}{ll}y=-1\\x=7\end{array}\right$

  Confirmação  

Seja  $x=7$  e  $y=-1$ :

    $\left\{\begin{array}{ll}x+y=6\\x-y=8\end{array}\right\Leftrightarrow$

$\Leftrightarrow\left\{\begin{array}{ll}7+(-1)=6\\7-(-1)=8\end{array}\right\Leftrightarrow$

$\Leftrightarrow\left\{\begin{array}{ll}7-1=6\\7+1=8\end{array}\right\Leftrightarrow$

$\Leftrightarrow\left\{\begin{array}{ll}6=6\;\;\;\;(Verdade)\\8=8\;\;\;\;(Verdade)\end{array}\right$

Resposta:  $(x\;;\;y)=(7\;;\;-1)$