Solve each system by eliminating one of the variables by addition or
subtraction.

1) x- y = 8

x + y = 12

eliminate one variable by adding the equations

2x = 20

divided by 2 on both sides

x = 10

substitute the value of x in the equation 1

10 - y = 8

-y = 8- 10

y =2

[x , y]

[10 , 2]

2) 2x - y = 4

3x + y = 6

eliminate one variable by adding the equations

5x = 10

x = 2

substitute the value of x in the equation

2(2) - y = 4

4 - y = 4

y = 0

[x ; y]

[2; 0]

3) x + 2y = 10

x + 4y = 14

multiply equation 1 by - 1

-x -2y = -10

x + 4y = 14

eliminate one variable by adding the equations

2 y = 4

y = 2

substitute the value of y in the equation 1

x + 2(2) = 10

x + 4 = 10

x = 6

[x ; y]

[6 ; 2]

4 ) 3x + y = 9

y = 3x + 6

simplify the expression

3x + y = 9

- 3x + y = 6

eliminate one variable by adding the equations

2y = 15

y = 15/2

substitute the value of y in equation 1

3x + 15/ 2 = 9

3x = 3/2

x = 1/2

[x ; y]

[1/2 ; 15/ 2]

5) 4x + 5y = 15

6x - 5y = 18

eliminate one variable by adding the equations

10 x = 33

× = 33/10

substitute the value of x in equation I

4 (33/10) + 5y = 15

66/5 + 5y =15

5y = 9/5

y = 9/25

[x ; y]

[33/10 ; 9/25]

6) 5x = 7y

x + 7y = 21

in equation I move the variable to the left

5x - 7y = 0

x + 7 y = 21

eliminate one variable by adding the equations

6x = 21

x = 7/2

substitute the value of x in the equation

5(7/2) = 7y

35/2 = 7y

5/2 = y

[x ; y ]

[7/2 ; 5/2 ]

iu

step-by-step explanation:

51

step-by-step explanation:

73-22=51 the   mass number minus the amount of protons gives you the amount of neutrons