Question

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

Answer 1

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