SOLUTION: Now I have this problem: solve the system by addition. 2x-4y=7 4x+2y=9 Ok so I subtract 2x-4x and get -2x then I do -4y+2y=-2y Now my problem looks like this; -2x+-2y=7+9=

Algebra ->  Linear-equations -> SOLUTION: Now I have this problem: solve the system by addition. 2x-4y=7 4x+2y=9 Ok so I subtract 2x-4x and get -2x then I do -4y+2y=-2y Now my problem looks like this; -2x+-2y=7+9=       Log On


   

Question 105387: Now I have this problem:
solve the system by addition.
2x-4y=7
4x+2y=9
Ok so I subtract 2x-4x and get -2x
then I do -4y+2y=-2y
Now my problem looks like this;
-2x+-2y=7+9=
-2x+-2y=16
Now what?
Answer by Earlsdon(6294) About Me  (Show Source):
You can put this solution on YOUR website!
Solve by addition: Note, the idea behind solving systems of equations is to eliminate one (or more) of the variables using any of the methods of addition, subtraction, substitution, etc.
2x-4y = 7
4x+2y = 9 To eliminate one the variables by addition, you first must multiply one or the other of the two equations by an integer so that you end up with the same number of one of the variable (either x or y) in both equations.
Since you are required to use addition, let's multiply the first equation by -2
-2(2x-4y = 7) to get:
-4x +8y = -14 Now add this equation to the second equation.
4x+2y = 9
----------
10y+=+-5 Notice that we have eliminated the x's Now divide both sides by 10.
y+=+-5%2F10 Simplify.
y+=+-1%2F2
Now we substitute this value of y into either one of the two original equations then solve it for x. Let's use the second equation:
4x%2B2y+=+9 Substitute y+=+-1%2F2
4x%2B2%28-1%2F2%29+=+9 Simplify.
4x+-1+=+9 Add 1 to both sides.
4x+=+10 Divide both sides by 4.
x+=+10%2F4 Simplify.
x+=+2.5
The solution is: (2.5, -1/2)
Let's see what the graph of these two equations looks like:
graph%28600%2C400%2C-5%2C5%2C-5%2C5%2C%281%2F2%29x-7%2F4%2C-2x%2B9%2F2%29
The solution is where the lines intersect.