Question

Resolva Sister de equação 5x-3y=12 -3x+y=-18

Answer 1

   5x-3y=12
   -3x+y=-18

y = 12 + 3x

5x - 3y = 12
5x - 3 ( 12 + 3x ) = -18
5x - 36 - 9x = -18
5x - 9x = -18 +36
 -4x = 18 
 x = 18/-4
  x = -4,5

- 3x + y = -18
- 3.(-4,5) + y = -18
  13,5 + y = -18
    y = -18 - 13,5
      y = - 31,5           ok

Answer 2

$\left \{ {{5x-3y=12} \atop {-3x+y=-18}} \right. multiplicando a debaixo por 3 temos: \left \{ {{5x-3y=12} \atop {-9x+3y=-54}} \right. cortando os valores de y temos: 5x-9x=12-54 / -4x=-42*(-1)/ 4x=42$
$x= \frac{42}{4} / x= \frac{21}{2} substituindo o valor de x na 1a equacao temos$
$5( \frac{21}{2})-3y=12/ 3y=-12 + 5( \frac{21}{2})/3y=-12+( \frac{5}{1}* \frac{21}{2} )/3y=-12+ \frac{31}{2}$
$3y= \frac{-12}{1}+ \frac{31}{2} /3y= \frac{7}{2}/ y= \frac{7}{2}* \frac{3}{1}/y= \frac{7}{6}$