Question

Решите систему уравнений:
{−2(4x+7y)+11x+21y=−30
{4(−4x−y)+25x+9y=−42

Answer 1

$left{{{-2(4x+7y)+11x+21y=-30}atop{4(-4x-y)+25x+9y=-42}}right.$
$left{{{-8x-14y+11x+21y=-30}atop{-16x-4y+25x+9y=-42}}right.\ left{{{3x+7y=-30}atop{9x+5y=-42}}right.\ left{{{3x+7y=-30big|(-3)}atop{9x+5y=-42}}right.\ +left{{{-9x-21y=90}atop{9x+5y=-42}}right.\ -21y+5y=90-42\ -16y=48\ y=-3\ x=frac{-30-7y}{3}=bigg[y=-3bigg]=frac{-30+21}{3}=-3\ left{{{x=-3}atop{y=-3}}right.\ ANSWER: (-3;-3)$