[tex]x + 2y = 0 \\ 2x - y = 5 \: \: \: | \times 2 \\ \\ x + 2y = 0 \\ 4x - 2y = 10 \\ \\ 5x = 10 \\ x = 10 \div 5 \\ x = 2 \\ \\ 4 \times 2 - 2y = 10 \\ 8 - 2y = 10 \\ 2y = 8 - 10 \\ 2y = - 2 \\ y = - 2 \div 2 \\ y = - 1 \\ \\ Ответ: \:(2 \: ; - 1\: )[/tex]
[tex]x - 6y = 15 \\ 4x + 3y = 6 \\ \\ x = 15 + 6y \\ 4(15 + 6y) + 3y = 6 \\ \\ 4(15 + 6y) + 3y = 6 \\ 60 + 24y + 3y = 6 \\ 27y = 6 - 60 \\ 27y = - 54 \\ y = - \frac{54}{27} \\ y = - 2 \\ \\ x = 15 + 6y = 15 + 6 \times ( - 2) = 15 - 12 = 3 \\ \\ Ответ: \:( 3 \: ; \: - 2 )[/tex]
[tex]4x + 5y = 3 \: \: \: | \times ( - 5) \\ 5x + 7y = 0 \: \: \: | \times 4 \\ \\ - 20x - 25y = - 15 \\ 20x + 28y = 0 \\ \\ 3y = - 15 \\ y = - \frac{15}{3} \\ y = - 5 \\ \\ 4x + 5 \times ( - 5) = 3 \\ 4x - 25 = 3 \\ 4x = 3 + 25 \\ 4x = 28 \\ x = \frac{28}{4} \\ x = 7 \\ \\ Ответ: \: ( 7 \: ; \: - 5)[/tex]