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Solving a system by the addition method. I am not sure how to do this. Can someone explain please

2007-10-12 07:04:49 · 7 answers · asked by brunettegirl 2 in Science & Mathematics Mathematics

7 answers

x - 2y = 9
x + 3y = -1
----------------
( subtracting second equation which is equivalent to changing the sign and adding)
x - 2y = 9
-x -3y = 1
----------------
-5y =10
and y= -2
so
x - 2(-2)= 9
x = 9 - 4 = 5

2007-10-12 07:09:13 · answer #1 · answered by Anonymous · 0 0

x-2y=9 (Equa 1)
x+3y=1 (Equa 2)
In order to find X and Y you need to cut down one of them and make a one equation with only one variable.So When we look at this we can clearly see that If you subtract Equa1 from 2, X will be cut off and you only get an equation with Y as follows
x+3y - (x-2y) = -1-9
x+3y - x+2y = -10
5y = -10
y = -2

You can find X in two different ways.either making another equation with only varialble X or by solving one of the equations with the value of y.I prefer 1st method.
So to cut off Y you have to have the same coefient in front of y so by multypling equa 1 from 3 and equa 2 from 2 you can have new two equations as follows
3x-6y=18 =eq3
2x+6y=-2=eq4

So then add them up together
it will be
6x=16
x=16/6
x=8/3

i think this will help you
regards

2007-10-12 15:02:35 · answer #2 · answered by Anonymous · 0 0

X - 2Y = 9
-(X + 3Y = -1)

X - 2Y = 9
-X - 3Y = 1
-----------------
-5Y = 10
Y = 10/-5 = -2

X - 2Y = 9
X - 2*(-2) = 9
X + 4 = 9
X = 5

2007-10-12 14:14:10 · answer #3 · answered by Trevor B 3 · 0 0

y= -2

2007-10-12 14:32:18 · answer #4 · answered by badbrown829 2 · 0 0

{x-2y=9
{x+3y=-1

I will time the first line on -1;

-x+2y=-9
x+3y=-1

Now I'm gonna sum the to lines

5y = -10
y = -2

x-2y=-9
x-2(-2)=-9
x+4=-9
x = -5

2007-10-12 14:13:09 · answer #5 · answered by ameti 2 · 0 0

Subtract the two formulae.
(x-x) + (3y-(-2y)) = (-1-9)
5y = -10
y= -2
x = 5

2007-10-12 14:10:20 · answer #6 · answered by Anonymous · 1 0

x - 2y = 9
- x - 3y + 1-------ADD
-5y = 10
y = - 2

x - 6 = - 1
x = 5

x = 5 , y = - 2

2007-10-13 13:42:59 · answer #7 · answered by Como 7 · 0 0

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