Question

Решите систему уравнений методом сложения:
3х +8y = 51
13x+y= 9​

Answer 1

$\left \{ {{3x+8y = 51} \atop {13x+y= 9}} \right. \\\left \{ {{3x+8y = 51} \atop {-104x-8y= -72}} \right. \\\\3x+8y+(-104x-8y)=51+(-72)\\-101x=-21\\x=\frac{21}{101} \\\\\frac{3*21}{101} +8y=51\\8y=51-\frac{63}{101} \\8y=\frac{5151-63}{101} \\\\8y=\frac{5088}{101}\\y=\frac{636}{101} = 6 \frac{30}{101} \\\\\left \{ {{x=\frac{21}{101}} \atop {y=6 \frac{30}{101}}} \right.$