Verified answer

а)

[tex]\displaystyle\bf\\\left \{ {{x - 2y = 3} \atop {3x - 4y = 13 }} \right. \\ \displaystyle\bf\\\left \{ {{x = 2y + 3} \atop {3(2y + 3) - 4y = 13 }} \right. \\ \\ 6y + 9 - 4y = 13 \\ 2y = 13 - 9 \\ 2y = 4 \\ y = 4 \div 2 \\ y = 2 \\ \\ x = 2 \times 2 + 3 \\ x = 4 + 3 \\ x = 7[/tex]

Ответ: ( 7 ; 2 )

б)

[tex]\displaystyle\bf\\\left \{ {{3x + 2y = 17 \: \: | \times( - 5)} \atop {13x + 5y = 59 \: \: | \times 2 }} \right. \\ \displaystyle\bf\\ + \left \{ {{ - 15x - 10y = - 85} \atop {26x + 10y = 118 }} \right. \\ \\ 26x - 15x = 118 - 85 \\ 11x = 33 \\ x = 33 \div 11 \\ x = 3 \\ \\ 3 \times 3 + 2y = 17 \\ 9 + 2y = 17 \\ 2y = 17 - 9 \\2 y = 8 \\ y = 8 \div 2 \\ y = 4[/tex]

Ответ: ( 3 ; 4 )