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)