Question

Помогите пожалуйста ​

Answer 1

1) Способ подстановки :

$\left \{ {{u+v=4} \atop {3u-5v=20}} \right. \\\\\left \{ {{u=4-v} \atop {3(4-v)-5v=20}} \right.\\\\\left \{ {{u=4-v} \atop {12-3v-5v=20}} \right. \\\\\left \{ {{u=4-v} \atop {12-8v=20}} \right. \\\\\left \{ {{u=4-v} \atop {-8v=8}} \right.\\\\\left \{ {{u=4-(-1)} \atop {v=-1}} \right.\\\\\left \{ {{u=5} \atop {v=-1}} \right.$

2) Способ сложения :

$\left \{ {{u+v=4}|*5 \atop {3u-5v=20}} \right.\\\\+\left \{ {{5u+5v=20} \atop {3u-5v=20}} \right.\\ ------\\8u=40\\\\u=5\\\\v=4-u=4-5=-1\\\\Otvet:\boxed{(5;-1)}$