[tex]x \times y = 7[/tex]
[tex]x \times y + 3y = 13 = > 7 + 3y = 13 = > 3y = 13 - 7 = > 3y = 6 = > y = 2[/tex]
[tex]x \times y + x + y = 14 = > 7 + x + 2 = 14 = > 9 + x = 14 = > x = 14 - 9 = > x = 5.[/tex]
[tex]x \times (x + 1) = 12 = > x {}^{2} + x = 12 = > x {}^{2} + x - 12 = 0 = > x = \frac{ - 1 - \sqrt{ {1}^{2} - 4 \times 1 \times ( - 12)} }{2 \times 1} . \: \: \: \: \: x = \frac{ - 1 + \sqrt{ {1}^{2} - 4 \times 1 \times ( - 12)} }{2 \times 1} = > x = \frac{ - 1 + \sqrt{49} }{2} . \: \: \: x = \frac{ - 1 - \sqrt{49} }{2} . = > x = \frac{ - 1 + 7}{2} . \: \: \: \: \: x = \frac{ - 1 - 7}{2} . = > \: \: \: x = - 4. \: \: \: x = 3.[/tex]
