solve the sytem by substitution 3x-y=-7 x+y=-9?

Answer 1

use the second equation
y=-x-9
3x + x +9 = -7
4x + 9 = -7
4x = -16
x= -4
then
-4 +y = -9
y=-5

Answer 2

the Simplest way is to solve the Second equation for y since you also see y all by itself in that first equation
x + y = -9
- x -x
subtract x from both sides gives y
+ y = - x - 9
or +y = - (x + 9)
Now plug in or Substitute this value of y into the First equation

3x - [- (x + 9) ] = -7

3x + x + 9 = - 7

4x + 9 = -7
subtract 9 from both sides
4x + 9 = - 7
-9 - 9

4x = - 16

divide both sides by 4

x = - 4

Now since we already found y = - ( x + 9 )

y = - ( -4 + 9 )
y = - ( +5)
y = - 5

CHECK x = -4 and y = - 5 by Plugging into either equations
3 ( -4) - (-5) = -7
- 12 + 5 = - 7 YES
-7 = -7

Answer 3

Substituting for x:

x = -9 - y

hence:

3(-9 - y) - y = -7 (1st equation)

-27 -3y - y = -7

-27 - 4y = -7

-4y = -20

-y = 5

y = -5

Substituting this into the 2nd equation:

x + (-5) = -9

x = -9 + 5

x = -4

Proof:

x + y = -9

-4 + (-5) = -9

3(-4) - (-5) = -7

-12 + 5 = -7

Answer 4

Hi,

Solve the 2nd equation for x:

x = -y - 9.

Now substitute this expression in place of x in the first equation and solve for y.

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

Plug -5 in for y and solve for x.

x + y = -9
x - 5 = -9
x = -4

So the solution is x = -4 and y = -5 for the point (-4,-5).

I hope that helps!! :-)

Answer 5

when it tells you to use a particular method to solve the problem, that means it is an exercise for you to practice using that method, even when another method may be quicker.

when you have two equations with two unknown variables, the substitution method is accomplished this way:

choose one of the equations and solve it for one of the variables. usually it doesn't matter which equation you pick or which variable you choose to solve for, but experience will tell when it will make your work easier to choose one equation and/or variable over the other.

in this example let's choose the first equation and solve it for y:
3x-y=-7
add 7 to both sides, then add y to both sides
3x+7=y
which can be reversed to y=3x+7

now that we know that y is the same thing as 3x+7
we substitute 3x+7 for every occurence of y in the second equation:

x + (3x+7) = -9

now our equation that had two variables (x and y) only has one variable, so we simplify and solve it for x

4x + 7 = -9
4x = -16
x = -4

so let's find y. we already determined that y=3x+7
therefore
y = 3(-4) + 7 = -12+7 = -5

so the solution is
x=-4, y=-5
or you could specify it as an ordered pair: (-4,-5)

Answer 6

It is like:

3x - y = -7 => 3x = y - 7 => x = (y-7)/3
Replace the value of x in the second equation:

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

Then, replace the value of y in any equation:

x - 5 = -9
x = -4

So, y = -5 and x = -4

Answer 7

3x - y = -7
x + y = -9
okay for substitution
3x-x =2x
-y -y = -2y
and
-7 +9 = +2
so the new equation well be
2x-2y = 2 this is answer the question you can also simply the equation by divide it by 2 we get
x - y =1

Answer 8

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

- 27 + 3y - y = - 7

- 20 + 2y = 0

- 20 = - 2 y

y = 10
x = - 19

Answer 9

ADD:-
4x = - 16
x = - 4
- 4 + y = - 9
y = - 9 + 4
y = - 5
x = - 4 , y = - 5