Решите систему уравнений A) y=3x-7 y=7-x Б)2y+x=7 15y-2x=27

Решите задачу:

$A$

$\left \{ {{y=3x-7} \atop {y=7-x}} \right. 7-x=3x-7 -x-3x=-7-7 -4x=-14 x= 3.5 y=3*3.5-7 y=10.5-7 y=3.5$

$B$

$\left \{ {{2y+x=7} \atop {15y-2x=27}} \right. \left \{ {{x=7-2y} \atop {15y-2x=27}} \right. 15y-2(7-2y)=27 15y-14+4y=27 15+4y=27+14 19y=41 y= 41/19 x=7- 2*(41/19)= 7-(82/19)= (133/19)-(82/19)=51/19$