Jawab:

1) x/4 + y/3 = 5/12

____________ ×12

=> 3x + 4y = 5

x/2 + y/1 = 1

_________ ×2

=> x + 2y = 2

3x + 4y = 5 |×1|

x + 2y = 2 |×2|

=> 3x + 4y = 5

2x + 4y = 4 -

________

x = 1

x + 2y = 2

1 + 2y = 2

2y = 1

y = ½

x + y

=> 1 + ½

=> 1½

2) 8/x + 3/y = 3

4/x + 9/y = 4

Misal :

a = 1/x

b = 1/y

=> 8a + 3b = 3 |×3|

4a + 9b = 4 |×1|

=> 24a + 9b = 9

4a + 9b = 4 -

__________

20a = 5

a = ¼

8a + 3b = 3

8(¼) + 3b = 3

3b = 3 - 2

b = ⅓

a = 1/x

¼ = 1/x

x = 4

b = 1/y

⅓ = 1/y

y = 3

=> x = 4

y = 3

3) 3x+y+z=7

2x+y-z=3

x+y+z=3

=>

1) 3x + y + z = 7

2x + y - z = 3 +

__________

5x + 2y = 10

2) 3x + y + z = 7

x + y + z = 3 -

__________

2x = 4

x = 2

3) 5x + 2y = 10

5(2) + 2y = 10

10 + 2y = 10

2y = 0

y = 0

4) 3x + y + z = 7

3(2) + 0 + z = 7

6 + 0 + z = 7

z = 7 - 6

z = 1

=> x = 2

y = 0

z = 1

4) 3x+2y+ z=12

4x +3y+2z=17

x+ y+3z= 5

=>

1) 3x + 2y + z = 12 |×2|

4x + 3y + 2z = 17 |×1|

=> 6x + 4x + 2z = 24

4x + 3y + 2z = 17 -

_____________

2x + y = 7

2) 3x + 2y + z = 12 |×3|

x + y + 3z = 5 |×1|

=> 9x + 6y + 3z = 36

x + y + 3z = 5 -

_____________

8x + 5y = 31

3) 2x + y = 7 |×4|

8x + 5y = 31 |×1|

=> 8x + 4y = 28

8x + 5y = 31 -

_________

-y = -3

y = 3

4) 8x + 5y = 31

8x + 5(3) = 31

8x = 31 - 15

8x = 16

x = 2

5) 3x + 2y + z = 12

3(2) + 2(3) + z = 12

6 + 6 + z = 12

z = 12 - 12

z = 0

=> x+y+z

=> 2 + 3 + 0

=> 5

5) x + y = 7

y - z = 9

y + z = 11

=> 1) y - z = 9

y + z = 11 +

_______

2y = 20

y = 10

2) y - z = 9

10 - z = 9

z = 1

3) x + y = 7

x + 10 = 7

x = -3

=> x²

=> (-3)²

=> 9

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