# Algebra

posted by Samantha

How do I solve this For (-x)?
(Do I just make -x equal 1 or 2?) I’m suppose to solve the equation by elimination. (Can someone give me steps to solving it and I’ll try to do it and you guys check my work?)
7x-9y=21
-x-18y=-3

1. Scott

multiply the 1st equation by -2, then add the result to the 2nd equation
... this will eliminate y

solve the subsequent equation for x

2. Samantha

I tried doing that but I think I went wrong somewhere because I did

7x-9y=21
-x-18y=-3

-2•7=-14
-2•9=-18
-2•21=-42

14x-18y=-42
-x-18y=-3

And got -x-0y=-3
-x=-45

...I know this is wrong, can someone help me

3. Scott

you lost the minus sign on the 14

you did this ... -2•9=-18
... the 9 was negative
... to give a positive 18 for cancelling with the -18 in the 2nd equation

should end up ... -15x = -45

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