Question

Решите систему уравнений {7x+4y=15
{3х+2у=3

Answer 1

{7x+4y=15
{3х+2у=3|*2
{7x+4y=15
{6х+4у=6
7x+4y-6x-4y=15-6
x=9
7*9+4y=15
63+4y=15
4y=15-63
4y=-48|:4
y=-12

Answer 2

$\left \{ {{7x+4y=15} \atop {3x+2y=3}} \right.$
$\left \{ {{x= \frac{15}{7} - \frac{4}{7}y } \atop {3x+2y=3}} \right.$
$3( \frac{15}{7} - \frac{4}{7}y)+2y=3$
y=-12
$x= \frac{15}{7} - \frac{4}{7}*(-12)=3$
x=9