Question

13. Розв'язати систему рiвнянь: 7x+3y=4 x-9y=8 13. ​

Answer 1

$\displaystyle\bf\\\left \{ {{7x+3y=4} \ |\cdot 3 \atop {x-9y=8}} \right. \\\\\\+\left \{ {{21x+9y=12} \atop {x-9y=8}} \right. \\----------\\22x=20\\\\x=\frac{10}{11} \\\\\\3y=4-7x=4-7\cdot\frac{10}{11} =4-\frac{70}{11} =4-6\frac{4}{11} =-2\frac{4}{11} \\\\\\y=-2\frac{4}{11} :3=-\frac{26}{11} \cdot\frac{1}{3} =-\frac{26}{33} \\\\\\Otvet \ : \ \Big(\frac{10}{11} \ \ ; \ \ -\frac{26}{33} \Big)$