Объяснение:

[tex]1)x + y = 4 \\ x - y = 5 \\ 2x = 9 \\ x = 4.5 \\ y = - 0.5 \\ 2)3x - 7y = 11 \\ 6x + 7y = 16 \\ 9x = 27 \\ x = 3 \\ 18 + 7y = 16 \\ y = \frac{2}{7} [/tex]

[tex]3)4x + 2y = 5 \\ 4x - 6y = - 7 \\ - 4x - 2y = - 5 \\ 4x - 6y = - 7 \\ - 8y = - 12 \\ y = \frac{12}{8} \\ 4x + 2 \times \frac{12}{8} = 5 \\ 4x + 3 = 5 \\ 4x = 2 \\ x = \frac{2}{4} [/tex]

[tex]3)6x + 7y = 2 \\ - 6x + 8y = - 92 \\ 15y = - 90 \\ y = - 6 \\ 6x - 42 = 2 \\ 6x = 44 \\ x = \frac{44}{6} [/tex]