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sherrywilliams
Jul 28, 2010, 08:13 AM
I am learning substitutions and eliminations and find this problem hard to solve. Can someone please help me solve the problem.

x+y=12
x-y=-6

ebaines
Jul 28, 2010, 09:00 AM
Here'e the process to use:

Step 1 - pick one of the equations (it doesn't matter which) and rearrange it to get either x or y by itself on one side of the equals sign (again, it doesn't matter which).

Step 2 - substitute that value for x or y back into the other equation. This gives the value of one of the unknowns

Step 3 - then substritute that value into the first equation, to find the valiue of the other unknown.

Here's an example - not exactly the same as yours, but it should help you understand the process:

Given:
x+y = 20
x-y = -22

Step 1: rearrange the first equation to get y by itself, by subtracting x from both sides:

x+y - x = 20 - x
y = 20 - x

Step 2: now substitute this value for y into the second equation:

x - y = -22
x - (20-x) = -22
2x - 20 = -22
2x = -22 + 20
2x = -2
x= -1

Step 3: now use this value of x = -1 in the first equation:

x + y = 20
-1 + y = 20
y = 20+1
y = 21

So the answer is: x = -1 and y = 21. Now, can you use this technique to solve your problem? Post back with what you get for an answer.