Question

{5x-3y=7
{x+2y=15 решите способом сложения

Answer 1

$left{{5x-3y=7} atop{x+2y=15 big | *(-5)}right.\ left{{5x-3y=7} atop{-5x-10y=-75}right.$

$+ left {{5x-3y=7}atop{-5x-10y=-75}right.\-3y-10y=-68\-13y=-68\ y=frac{68}{13}$
$left {{y=frac{68}{13}}atop{x+2y=15}right.\ left {{y=frac{68}{13}}atop{x=15-2y }right.$

$left { {y=frac{68}{13}}atop {x=15-2*frac{68}{13}}right.$

$left { {y=frac{68}{13}} atop{x=15-frac{136}{13}}right.$

$left{ {y=frac{68}{13}}atop{x=frac{59}{13} }right.$

$Answer: (frac{59}{13};frac{68}{13})$

Answer 2

{5x-3y=7
{x+2y=15      I*-5

{5x-3y=7
{-5x-10y=-75
сложим
-13у=-68
у=5 3/13
х=15-2у=15-10 6/13=4 7/13
(4 7/13;5 3/13)