Question

помогите решить хоть два примера пю​

Answer 1

Решаем способом сложения:

х-7у=0

12х+у=17  (умножим на  7)

х-7у=0

84х+7у=119

85х  =  119;           х=1,4

1,4-7у=0;  7у=1,4;  у=0,2

Ответ: (1,4;  0,2)

5х-у=1 (умножим на 3)

х+3у=5

15х-3у=3

х+3у=5

16х   =  8;                  х=0,5

0,5+3у=5;  3у=4,5;   у=1,5

Ответ: (0,5;  1,5)

3х+5у=2 (умножим на -4)

4х+7у=6 (умножим на 3)

-12х-20у=-8

12х+21у=18  

                                    у = 10

3х+5*10=2;    3х=-48; х=-16

Ответ: (-16;   10)

Answer 2

$\displaystyle\left \{ {{x-7y=0} \atop {12x+y=17} } \right.\\\\\\\displaystyle\left \{ {{x=7y} \atop {12\cdot7y+y=17} } \right.\\\\\\\displaystyle\left \{ {{x=7y} \atop {84y+y=17} } \right.\\\\\\\displaystyle\left \{ {{x=7y} \atop {84y+y=17} } \right.\\\\\\\displaystyle\left \{ {{x=7\cdot 0,2} \atop {y=0,2} } \right.\\\\\\\displaystyle\left \{ {{x=1,4} \atop {y=0,2} } \right.\\\\\\Otvet:\boxed{(1,4 \ ; \ 0,2)}$

$2) \ \displaystyle\left \{ {5x-y=1} \atop {x+3y=5} } \right. \\\\\\\displaystyle\left \{ {{y=5x-1} \atop {x+3\cdot(5x-1)=5} } \right. \\\\\\\displaystyle\left \{ {{y=5x-1} \atop {x+15x-3=5} } \right.\\\\\\\displaystyle\left \{ {{y=5x-1} \atop {16x=8} } \right. \\\\\\\displaystyle\left \{ {{y=5\cdot0,5-1} \atop {x=0,5} } \right. \\\\\\\displaystyle\left \{ {{y=1,5} \atop {x=0,5} } \right.\\\\\\Otvet:\boxed{(0,5 \ ; \ 1,5)}$

$3) \ \displaystyle\left \{ {{9x+2y=16} \atop {3x-5y=11} \ |\cdot(-3) } \right.\\\\\\+ \displaystyle\left \{ {{9x+2y=16} \atop {-9x+15y=-33} } \right.\\----------\\17y=-17\\\\y=-1\\\\3x=11+5y=11+5\cdot(-1)=11-5=6\\\\x=2\\\\Otvet:\boxed{(2 \ ; - 1)}$

$4) \ \displaystyle\left \{ {{3x+5y=2} \ |\cdot4 \atop {4x+7y=6 \ |\cdot(-3) } \right.\\\\\\+ \displaystyle\left \{ {{12x+20y=8} \atop {-12x-21y=-18} } \right.\\-----------\\-y=-10\\\\y=10\\\\3x=2-5y=2-5\cdot10=2-50=-48\\\\x=-16\\\\Otvet:\boxed{(-16 \ ; \ 10)}$