Explicación paso a paso:
[tex]3x + 5y = 12 \\ 3x = 12 - 5y \\ x = \frac{12 - 5y}{3} [/tex]
[tex]5x + 3y = 4 \\ 5x = 4 - 3y \\ x = \frac{4 - 3y}{5} [/tex]
[tex] \frac{4 - 3y}{5} = \frac{12 - 5y}{3} \\ 12 - 9y = 60 - 25y \\ - 60 + 12 = - 25y + 9y \\ - 48 = - 16y \\ 16y = 48 \\ y = \frac{48}{16} = 3[/tex]
[tex]x = \frac{4 - 3y}{5} = \frac{4 - 3 \times 3}{5} = \frac{4 - 9}{5} = \frac{ - 5}{5} = - 1[/tex]
[tex]3 \times ( - 1) + 5 \times 3 = 12 \\ 5 \times ( - 1) + 3 \times 3 = 4[/tex]
