Question

Решить систему уравнений x+y=7 5x-7y=11

Answer 1

$left { {{x+y=7} atop {5x-7y=11}} right.$

 

$left { {{x=7-y} atop {5(7-y)-7y=11}} right.$

 

$5(7-y)-7y=11$

 

$35-5y-7y=11$

 

$35-12y=11$

 

$12y=35-11$

 

$12y=24$

 

$y=24:12$

 

$y=2$

 

$x=7-y=7-2=5$

 

$left { {{x=5} atop {y=2}} right.$

 

Проверка:

 

$left { {{5+2=7} atop {5cdot5-7cdot2=11}} right.$

 

$left { {{7=7} atop {25-14=11}} right.$

 

$left { {{7=7} atop {11=11}} right.$