1)

[tex]\displaystyle\bf\\ + \left \{ {{2x + y = 3} \atop {2x - y = 5}} \right. \\ \\2x + 2x = 3 + 5 \\ 4x = 8 \\ x = 8 \div 4 \\ x = 2 \\ \\ 2 \times 2 + y = 3 \\ 4 + y = 3 \\ y = 3 - 4 \\ y = - 1[/tex]

Ответ: ( 2 ; - 1 )

2)

[tex]\displaystyle\bf\\ + \left \{ {{2x - 8y = 7} \atop { - 2x + 7y = 5}} \right. \\ \\7y - 8y = 7 + 5 \\ - y = 12 \\ y = - 12 \\ \\ 2x - 8 \times ( - 12) = 7 \\ 2x + 96 = 7 \\ 2x = 7 - 96 \\ 2x = - 89 \\ x = - 89 \div 2 \\ x = - 44.5[/tex]

Ответ: ( - 44,5 ; - 12 )

3)

[tex]\displaystyle\bf\\\left \{ {{4x + 5y = 7} \atop {2x - 3y = - 2 \: \: | \times ( - 2)}} \right. \\ \displaystyle\bf\\ + \left \{ {{4x + 5y = 7} \atop { - 4x + 6y = 4}} \right. \\ \\5y +6 y = 7 + 4 \\ 11y = 11 \\ y = 11 \div 11 \\ y = 1 \\ \\ 2x - 3 \times 1 = - 2 \\ 2x = - 2 + 3 \\ 2x = 1 \\ x = 1 \div 2 \\ x = 0.5[/tex]

Ответ: ( 0,5 ; 1 )