Объяснение:

1.

{у=9х+5

{у=23х-6

23х-6=9х+5

23х-9х=5+6

14х=11

х=11/14

у=9•11/14+5

у=99/14+5

у=169/14

(11/14;169/14)

2.

{у=13х-7

{у=5х+24

13х-7=5х+24

13х-5х=24+7

8х=31

х=31/8

у=5•31/8+24

у=155/8+24

у=347/8

(31/8;347/8)

3.

{у= -8х-15

{у= -21х+11

-8х-15= -21х+11

-8х+21х=11+15

13х=26

х=2

у= -8•2-15

у= -16-15

у= -31

(2; -31)

4.

{5х-3у=14

{2х+у=10 у=10-2х

5х-3(10-2х)=14

5х-30+6х=14

11х=14+30

11х=44

х=44:11

х=4

у=10-2•4

у=10-8

у=2

(4;2)

5.

{х+5у=35 х=35-5у

{3х+2у=27

3(35-5у)+2у=27

105-15у+2у=27

-13у=27-105

-13у= -78

у= -78:(-13)

у=6

х=35-5•6

х=35-30

х=5

(5;6)

6.

{7х-2у=15

{2х+у=9 у=9-2х

7х-2(9-2х)=15

7х-18+4х=15

11х=15+18

11х=33

х=33:11

х=3

у=9-2•3

у=9-6

у=3

(3;3)

7.

{2х-у=2 у=2х-2

{3х-2у=3

3х-2(2х-2)=3

3х-4х+4=3

-х=3-4

-х= -1

х=1

у=2•1-2

у=2-2

у=0

(1;0)

8.

{5у-х=6 х=5у-6

{3х-4у=4

3(5у-6)-4у=4

15у-18-4у=4

11у=4+18

11у=22

у=22:11

у=2

х=5•2-6

х=10-6

х=4

(4;2)

9.

{3х+4у=55

{7х-у=56 у=7х-56

3х+4(7х-56)=55

3х+28х-224=55

31х=55+224

31х=279

х=279:31

х=9

у=7•9-56

у=63-56

у=7

(9;7)

10.

{у= -11х+9

{у= -21х+11

-11х+9= -21х+11

-11х+21х=11-9

10х=2

х=2:10

х=0,2

у= -11•0,2+9

у= -2,2+9

у=6,8

(0,2;6,8)

11.

{х+3у=2 х=2-3у

{2х+3у=7

2(2-3у)+3у=7

4-6у+3у=7

-3у=7-4

-3у=3

у=3:(-3)

у= -1

х=2-3•(-1)

х=2+3

х=5

(5;-1)

12.

{4у-х=11 х=4у-11

{6у-2х=13

6у-2(4у-11)=13

6у-8у+22=13

-2у=13-22

-2у= -9

у=4,5

х=4•4,5 -11

х=18-11

х=7

(7;4,5)

13.

{х-2у=3 х=3+2

{5х+у=4

5(3+2у)+у=4

15+10у+у=4

11у=4-15

11у= -11

у= -11:11

у= -1

х=3+2•(-1)

х=3-2

х=1

(1;-1)

14.

{3у+8х=5

{у+4х=2 у=2-4х

3(2-4х)+8х=5

6-12х+8х=5

-4х=5-6

-4х= -1

х= -1:(-4)

х=0,25

у=2-4•0,25

у=2-1

у=1

(0,25;1)

15

{5х+у=3 у=3-5х

{3х-2у=7

3х-2(3-5х)=7

3х-6+10х=7

13х=7+6

13х=13

х=13:13

х=1

у=3-5х

у=3-5•1

у=3-5

у= -2

(1;-2)