Question

Se (3 -1). (x) = 4. (1), determine o valor de x+y.
     (  1 3)  (y)       ( 2)

Answer 1

$\left[\begin{array}{ccc}3&-1\\1&3\end{array}\right] * \left[\begin{array}{ccc}x\\y\end{array}\right] = 4* \left[\begin{array}{ccc}1\\2\end{array}\right]       \left[\begin{array}{ccc}3x-y\\x+3y\end{array}\right] = \left[\begin{array}{ccc}4\\8\end{array}\right]$

3x-y = 4 
x+3y = 8 

x = 8-3y

Vamos substituir na primeira equação: 
3*(8-3y)-y = 4
24-9y-y = 4 
24-10y = 4 
-10y = 4-24
-y = -20/10 
-y = -2
 y = 2

x vale 8-3y, logo
x = 8-3*2
x = 8-6
x = 2

x+y = 2+2 = 4