Question

se o par ordenado x+y=-3 e 2x-y=-1 qual o resultado

Answer 1

{x+y= -3 -> corta os "y" pois os sinais são
{2x-y= -1 opostos
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3x= -4
x= -4/3

Answer 2

$Resolvendo\ pela\ regra\ de\ Cramer:\\\\ \left \{ {{x+y=-3} \atop {2x-y=-1}} \right.\\\\ A=\left[\begin{array}{ccc}1&1\\2&-1\\\end{array}\right] =-1-2=-3\\\\ A_x=\left[\begin{array}{ccc}-3&1\\-1&-1\\\end{array}\right]=3+1=4\\\\A_y=\left[\begin{array}{ccc}1&-3\\2&-1\\\end{array}\right]=-1+6=5\\\\ x=\frac{detA_x}{detA}= \frac{4}{-3}= \| \ \frac{-4}{3}\ \|\\\\ y= \frac{detA_y}{detA}=\frac{5}{-3}= \| \ \frac{-5}{3}\ \|$

$Resolvendo\ de\ forma\ trivial\ (e\ pr\acute atica):\\\\ \left \{ {{x+y=-3} \atop {2x-y=-1}} \right.\\\\ Somando\ ambas,\ teremos:\\\\ x+y+2x-y=-3-1\\ 3x=-4\\ \| \ x= \frac{-4}{3}\ \| \\\\ x+y=-3\\ \frac{-4}{3}+y=-3\\ y= -3+\frac{4}{3}\\ y=\frac{-9+4}{3}\\ \| \ y= \frac{-5}{3}\ \|$