Question

помогите пожалуйста решить 1,3,5.
алгебраическим сложением.​
очень нужно

Answer 1

$\displaystyle\bf\\1)\\\\\left \{ {{x+5y=7} \ |\cdot(-3) \atop {3x-2y=4}} \right. \\\\\\+\left \{ {{-3x-15y=-21} \atop {3x-2y=4}} \right. \\ -----------\\-17y=-17\\\\y=1\\\\x=7-5y=7-5\cdot 1=7-5=2\\\\Otvet: \ (2 \ ; \ 1)\\\\\\3)\\\\\left \{ {{x+12y=11} \ \atop {5x-3y=3}|\cdot 4 \ } \right. \\\\\\+\left \{ {{x+12y=11} \atop {20x-12y=12}} \right. \\ -----------\\21x=23\\\\x=1\frac{2}{21} \\\\3y=5x-3=5\cdot\frac{23}{21} -3=6\frac{2}{21}-3=3\frac{2}{21}$

$\displaystyle\bf\\y=3\frac{2}{21} :3=1\frac{2}{63} \\\\\\Otvet: \ \Big(1\frac{2}{21} \ ; \ 1\frac{2}{63} \Big)\\\\\\5)\\\\\left \{ {{2x-2y=0} \ |\cdot(-1) \atop {3x-2y=5}} \right. \\\\\\+\left \{ {{-2x+2y=0} \atop {3x-2y=5}} \right. \\---------\\x=5\\\\2y=2x=2\cdot 5=10\\\\y=10:2=5\\\\Otvet: \ (5 \ ; \ 5)$