Question

нужно решить как можно скорее

Answer 1

1) Сложим первое уравнение с третьим :

$\displaystyle\bf\\\left \{ {{x_{1} +x_{2} - x_{3}=-2 \ |\cdot (-4) } \atop {4x_{1} +4x_{2} -3x_{3} =-5}} \right. \\\\\\+\left \{ {{-4x_{1} -4x_{2} +4x_{3}=8 } \atop {4x_{1} +4x_{2} -3x_{3} =-5}} \right.\\ ------------\\x_{3}=3$

2) Сложим первое со вторым :

$\displaystyle\bf\\\left \{ {{x_{1} +x_{2} - x_{3}=-2 } \atop {3x_{1} -x_{2} +2x_{3} =9}} \right. \\\\\\\left \{ {{x_{1} +x_{2} - 3=-2 } \atop {3x_{1} -x_{2} +6 =9}} \right. \\\\\\+\left \{ {{x_{1} + x_{2} =1} \atop {3x_{1}-x_{2} =3}} \right.\\ ---------\\ 4x_{1}=4\\\\x_{1} =1\\\\x_{2} =1-x_{1} =1-1=0\\\\Otvet \ : \ \Big(1 \ ; \ 0 \ ; \ 3\Big)$