solve by the folling system of equations by subsitution. show your work x + y = 7, =3x + y = -1?

Question

thanks

Answer 1

The question doesn't really make sense as it is. Here is the answer ignoring the equals sign just before the 3x

x + y = 7, so y = 7 - x

3x + y = -1
3x + 7 - x = -1
2x + 7 = -1
2x = -8
x = -4

y = 7 - (-4)
y = 11

x = -4, y = 11

If the equals sign before the 3x is meant to be a negative sign

x + y = 7, so y = 7 - x

-3x + y = -1
-3x + 7 - x = -1
-4x + 7 = -1
-4x = -8
x = 2

y = 7 - 2
y = 5

x = 2, y = 5

Answer 2

Let x + y = 7 is a
3x + y = -1 is b

if x + y = 7
then x = 7 - y

replace the x = 7 - y into b

3 x + y = -1
3 (7 - y) + y = -1
21 - 3y + y = -1
21 - 2y = -1
21 + 1 = 2y
22 = 2y
22 / 2 = y
11 = y

replace y = 11 into a

x + y = 7
x + 11 = 7
x = 7 - 11
x = -4

Hence, x = -4, y = 11

Answer 3

x + y = 7- - - - - - Equation 1
3x + y = - 1- - - - Equation 2
- - - - - - - -

Substitute Method equation 1

x + y = 7

x + y - x = 7 - x

y = 7 - x

The answr is y = 7 - x

Insert the y value into equation 2

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

3x + y = - 1

3x + 7 - x = - 1

2x + 7 = - 1

2x + 7 - 7 = - 1 - 7

2x = - 8

2x/2 = - 8/2

x = - 4

The answr is x = - 4

Insert the x value into equation 1

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

x + y = 7

- 4 + y = 7

- 4 + y + 4 = 7 + 4

y = 11

The answer is y = 11

Insert the y value ihto equation 1

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

Check for equatioh 1

x + y = 7

- 4 + 11 = 7

7 = 7

- - - - - - - - - - -

Check for equation 2

3x + y = - 1

3( - 4) + 11 = - 1

- 12 + 11 = - 1

- 1 = - 1

- - - - - - - - - -

The solution set is { - 4, 11 }

- - - - - -s-

Answer 4

x + y = 7
3x + y = -1

x + y = 7 => y = 7 - x

3x + y =-1 => 3x + 7 - x= -1 => 2x= -1 -7 => 2x=-8 => x= -4
x=-4 => y=7 - (-4)=7+4=11