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.