Question

{3x+7y=15; {x-3y=-3.

Answer 1

$3x + 7y = 15 \ x - 3y = - 3 \ \ 3x + 7y = 15 \ 3x - 9y = - 9 \ \ + 7y - ( - 9y) = 15 - ( - 9) \ x = - 3 + 3y \ \ 16y = 24 \ x = 3y - 3 \ \ y = 1.5 \ x = 4.5 - 3 = 1.5$
Ответ: (1.5; 1.5)

Answer 2

опечатка во 2 шаге

Answer 3

Исправлено

Answer 4

$left { {{3x+7y=15} atop {3x-9y=-9}} right.$ (1)

$left { {{9x+21y=45} atop {7x-21y=-21}} right.$ (2)

из (1): $16y=24, y=1.5$

из (2): $16x=24, x=1.5$

Ответ: (1.5; 1.5)