Question

Решите систему методом подстановки
х+ 3у=9 и 3х-у= 7

Answer 1

$\left \{ {{x+3y=9} \atop {3x-y=7}} \right. ; \left \{ {{x=9-3y} \atop {3x-y=7}} \right. ; \left \{ {{x=9-3y} \atop {3*(9-3y)-y=7}} \right. ; \left \{ {{x=9-3y} \atop {27-9y-y=7}} \right. ; \\ \left \{ {{x=9-3y} \atop {-10y=-20}} \right. ; \left \{ {{x=9-3y} \atop {y=2}} \right. ; \left \{ {{x=9-3*2} \atop {y=2}} \right. ; \left \{ {{x=3} \atop {y=2}} \right.$
Ответ: (3;2)

Answer 2

$\left \{ {{x+3y=9} \atop {3x-y=7}} \right.$ $\left \{ {{3y=-x+9} \atop {3x-y=7}} \right.$ $\left \{ {{y=- \frac{1}{3}x+3 } \atop {3x-( -\frac{1}{3}x+3)=7}} \right.$ $\left \{ {{y=- \frac{1}{3}x+3 } \atop {3x+ \frac{1}{3}x-3=7 }} \right.$$\left \{ {{y=- \frac{1}{3}x+3 } \atop { \frac{10}{3}x=10 }} \right.$$\left \{ {{y=2} \atop {x=3}} \right.$
Ответ: (3;2)