Question

resolva o sistema:

2) {x+y=20
{x-3y=-12


pfvr me respondem essa???​

Answer 1

Resposta:

.     S  =  {(x,  y)}  =  {(12,  8)}

Explicação passo a passo:

.

.      x  +  y  =  20   ==>   y  =  20 - x             (troca na outra)

.      x  -  3y =  - 12

.

==>    x  -  3 . (20 - x)  =  - 12

.         x  -  60  +  3x  =  - 12

.         x  +  3x  =  - 12  +  60

.         4x  =  48

.         x  =  48  :  4

.         x  =  12                        y  =  20  -  x

.                                             y  =  20 -  12

.                                             y  =  8

.

(Espero ter colaborado)

Answer 2

One may value alternative solution in order to get a better comprehension.

Thus:

Multiplying the second equation by (- 1) yields:

{x + y = 20

{- x + 3y = 12

Making the sum of LHS and RHS of both equation equals to each other:

(LHS means left hand side, and RHS means right hand side).

x + y + (- x + 3y) = 20 + (12)

x - x + y + 3y = 20 + 12

0 + 4y = 32

4y = 32

y = 32/4

y = 8

By substituting y = 8 in the first or second equation we get:

In the 1st,

x + y = 20

x + 8 = 20

x = 20 - 8

x = 12

Or, in the 2nd,

x - 3y = - 12

x - 3(8) = - 12

x - 24 = - 12

x = - 12 + 24

x = 12

Therefore, the solution to your system is $\displaystyle \left \{ {{x=12} \atop {y=8}} \right.$.

Enjoy your studies, ma dear.