1. {6х+3=5х–20у–16
{6х–9у–6х=8–у
{х+20у=–19
{–8у=8
у=–1
х+20•(–1)=–19
х=1
Ответ: (1;-1)
2. {(х+3)/2–(у–4)/7=1 |•14
{6у–х=5
{7(х+3)–2(у–4)=14
{х=6у–5
{7х+21–2у+8=14
{х=6у–5
7(6у–5)–2у=–15
42у–35–2у=–15
40у=20
у=1/2
х=(6•1)/2–5=–2
Ответ: (–2;1/2)
3. Домножим первое уравнение на 24, второе на 12:
{3(х+у)+4(х–у)=96
{3(3х+у)–4(2х–5у)=60
{3х+3у+4х–4у=96
{9х+3у–8х+20у=60
{7х–у=96
{х+23у=60
{у=7х–96
{х+23(7х–96)=60
х+161х–2208=60
162х=2268
х=14
у=7•14–96=2
Ответ: (14;2)