Question

25 с системой уровнений {3x-y=17 {2x-3x=-7

Answer 1

$\left \{ {{3x-y=17} \atop {2x-3x=-7}} \right.$

$\left \{ {{3x-y=17} \atop {-x=-7}} \right.$

$\left \{ {{3x-y=17} \atop {x=7}} \right.$

x=7

3*7-y=17
-y=-21+17
-y=-4
y=4

x=7
y=4

ответ: (7;4)

Answer 2

$\displaystyle \left \{ {{3x-y=17} \atop {2x-3x=-7}} \right. \\ \\ \left \{ {{y=3*7-17} \atop {x=7}} \right. \\ \\ \left \{ {{y=4} \atop {x=7}} \right.$

ответ: {7; 4}

Если, все-таки, во втором уравнении так: 2х - 3у = -7, то:

$\displaystyle \left \{ {{3x-y=17} \atop {2x-3y=-7}} \right. \\ \\ \left \{ {{y=3x-17} \atop {2x-3(3x-17)=-7}} \right. \\ \\ 2x-9x+51=-7 \\ 7x=58 \\ \\ x=8 \frac{2}{7}; \\ y=3*8 \frac{2}{7}-17=24 \frac{6}{7}-17=7 \frac{6}{7}$

ответ:{8 2/7; 7 6/7}