Solve the system by substitution. 3x – y = –7, x + y = –9?

Question

Solve the system by substitution. 3x – y = –7, x + y = –9

Answer 1

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

Now sub this value of y into the second equation:
x + y = -9
x + (7 + 3x) = -9

Solve for x
x + 7 + 3x = -9
4x = -9 - 7
4x = -16
x = -4

Now sub this value of x into the first equation:
3x - y = -7
3(-4) - y = -7
- y = -7 +12
y = -5

Hope this helps :)

Answer 2

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x - 2y = 9 -3x + y = -7 I'm going to use the elimination method, multiply the bottom equation by 2 to cancel the y's and add it to the first one. x - 2y = 9 [-3x + y = -7]*2 x - 2y = 9 -6x + 2y = -14 ------------------- Add them and you get -5x = -5 x = 1 Substitute this value into any of the 2 original equations to solve for y x - 2y = 9 1 - 2y = 9 -2y = 8 y = -4 The solution is (1 , - 4)

Answer 3

x + y = -9

Therefore

y = - 9 - x

Substitution

3x - (-9 - x) = -7

Distribute the -1

3x + 9 + x = -7

Combine like

4x + 9 = -7

Move the 9 with inverse operations

4x = - 16

Move the 4 with inverse operations

x = - 4

substitute -4 for x in x + y = - 9

-4 + y = -9

y = -5

check:

3 * -4 - - 5 = -7

-12 +5 = -7

-7 = -7

therefore
y = -5
x = -4

Answer 4

To solve the system by substitution, we need to isolate one of the variables. Let's use the first equation:

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

Now we can substitute the (7+3x) into the second equation for y:

x + 7 + 3x = -9

4x + 7 = -9

4x = -16

x = -4

Great, put that -4 back into either equation to find y, and

y = -5

Your solution (-4,-5)

that's it! :)

Answer 5

What that means is that you solve for one variable in one of the equations and use that answer as a substitute in the other equation. For example...

x + y = 2
2x - y = 10

Solve the first equation for X
x = 2 - y

Now use (2-y) wherever you see X in the second equation and solve.

Answer 6

3x-y = -7 x+y = -9

so we can deduct that x = -9 - y

so 3(-9-y)-y = -7

-27-4y= -7

-4y = 20

y = -5 and then u put this into x+y = -9 so x = -4 =] ar har

Answer 7

Algebraically solve one of them for y and then plug in what y= in for y into the the other equation. Solve for x, then plug that number in for x and solve for y.

Answer 8

3x-y=-7
x+y=-9

x=-9-y
3(-9-y)-y=-7
-27-3y-y=-7
-4y=20
y=-5

x+-5=-9
x=-4