SOLUTION: I am having trouble solving the system of equations by graphing.I can never seem to choose the right numbers to replace the variables with. For example: 2x - 6y = 42 3x - 9y = -

Algebra ->  Graphs -> SOLUTION: I am having trouble solving the system of equations by graphing.I can never seem to choose the right numbers to replace the variables with. For example: 2x - 6y = 42 3x - 9y = -      Log On


   

Question 147313: I am having trouble solving the system of equations by graphing.I can never seem to choose the right numbers to replace the variables with. For example:
2x - 6y = 42
3x - 9y = -15
I keep getting (8, -4) for the ordered pair but this in not correct. Can you help me figure this out please.
Answer by jim_thompson5910(35256) About Me  (Show Source):
You can put this solution on YOUR website!

Start with the given system of equations:
system%282x+-+6y+=+42%2C3x+-+9y+=+-15%29


3%282x+-+6y+%29=3%28+42%29 Multiply the both sides of the first equation by 3.


6x-18y=126 Distribute and multiply.


-2%283x+-+9y+%29=-2%28+-15%29 Multiply the both sides of the second equation by -2.


-6x%2B18y=30 Distribute and multiply.


So we have the new system of equations:
system%286x-18y=126%2C-6x%2B18y=30%29


Now add the equations together. You can do this by simply adding the two left sides and the two right sides separately like this:


%286x-18y%29%2B%28-6x%2B18y%29=%28126%29%2B%2830%29


%286x%2B-6x%29%2B%28-18y%2B18y%29=126%2B30 Group like terms.


0x%2B0y=156 Combine like terms. Notice how the x and y terms cancel out.


0=156Simplify.


Since 0=156 is never true, this means that there are no solutions. So the system is inconsistent.