[MOVED] question driving me insane (solving systems)

[frankl5297]

Use elimination to solve the following system of equations:

. . .y = 7 - x
. . .x - y = -3

I have no idea and my mom (who is pretty much my math expert) can't figure it out. Please help!

 

[Mrspi]

Re: question driving me insane

Use elimination to solve the system of equations.

y=7-x
x-y= -3


I have no idea and my mom which is pretty much my math expert can't figure it out and i have no math skills please help!

Well, if you HAVE to use the elimination method (which isn't the easiest way to go on this one), then get both equations into the same form....which is usually with both variable terms on one side, and the constant term on the other side.

Add x to both sides of the first equation:
y = 7 - x
y + x = 7 - x + x
y + x = 7

or,
x + y = 7

Now, your two equations are
x + y =7
x - y = -3

Note that if you ADD the two equations together, the y terms will "disappear" because y + (-y) is 0:

x + y = 7
x - y = -3
--------------
2x + 0y = 4

2x = 4

Now, divide both sides of the equation by 2:

x = 2

Ok...now, you know that x = 2. You also know that
x + y = 7

Substitute 2 for x, and solve for y....

 

[skeeter]

Re: question driving me insane

Use elimination to solve the system of equations.

y=7-x
x-y= -3

just "add" the two equations together ...

    y =  7 - x
x - y = -3
---------------
x      = 4 - x

2x = 4

x = 2

now use x = 2 in either of the original equations to solve for y