Question

a)

{x+5y=13

3x+y=11

b)

{4x-3y=30

x+y=4

c)

{8x-y=2

5x+4y=1

Answer 1

{ x=13-5y

3(13 -5y) + y =11

{ x=13-5y

39 - 15 y +y = 11

{ x=13-5y

-14y = 11-39

{ x=13-5y

-14 y = -28 / * (-1)

{ x=13-5y

14y = 28 / :14

{ x=13-5y

y = 2

 

{ x=13-5y

 

x = 13 - 5*2 = 3

y = 2 i x = 3

 

 

b) {4x-3y=30

x = 4- y

{ 4 ( 4- y) - 3y = 30

x = 4- y

{16 - 4y - 3y = 30

x = 4- y

{- 7y = 14 / ; -7

x = 4- y

{  y = -2

x = 4- y

 

x = 4 - (-2) = 4 +2 = 6

 

x = 6 a y = -2

 

 

 

 

Answer 2

a)

x+5y=13 |*(-3)

3x+y=11

 

-3x-15y=-39

3x+y=11

----------------

-14y=(-28)|:(-14)

y=2

 

3x+2=11

3x=9|:3

x=3

 

y=2

x=3

 

b)

4x-3y=30

x+y=4 |*3

 

4x-3y=30

3x+3y=12

-------------

7x=42|:7

x=6

 

3*6+3y=12

3y=12-18

3y=-6|:3

y=-2

 

x=6

y=-2

 

c)

8x-y=2|*4

5x+4y=1

 

32x-4y=8

5x+4y=1

--------------

37x=9|:37

x=9/37

 

5*9/37=4y=1

a to już do obliczenia samemu :D