1) {х=5–у
{3(5–у)–у=11
15–3у–у=11
–4у=–4
у=1
х=5–1=4
Ответ: (4;1)
2) {х=15+3у
{4(15+3у)+3у=0
60+12у+3у=0
15у=–60
у=–4
х=15+3•(–4)=3
Ответ: (3;–4)
3) {у=3х–2
{х+2(3х–2)=10
х+6х–4=10
7х=14
х=2
у=3•2–2=4
Ответ: (2;4)
4) {х=6+3у
{2у–5(6+3у)=–4
2у–30–15у=–4
–13у=26
у=–2
х=6+3•(–2)=0
Ответ: (0;–2)
5) {х=2+2у
{3у–2(2+2у)=1
3у–4–4у=1
–у=5
у=–5
х=2+2•(–5)=–8
Ответ: (–8;–5)
6) {1+2х–2у=3х–4у
{10–4х–4у=3у–3х
{–х+2у=–1
{–х–7у=–10
{х=2у+1
{х=10–7у
2у+1=10–7у
9у=9
у=1
х=2•1+1=3
Ответ: (3;1)
7) {х/3–у/9=3 |•9
{х/6+у/3=–2 |•6
{3х–у=27
{х+2у=–12
{у=3х–27
{х+2(3х–27)=–12
х+6х–54=–12
7х=42
х=6
у=3•6–27=9
Ответ: (6;9)