Either I forgot or never did learn to do it well. I need to solve the following system:
$$9a+3b+c=0$$ $$25a-5b+c=0$$ $$a-b+c=12$$
Google shows me this page with some instructions: http://www.jcoffman.com/Algebra2/ch3_6.htm, I decided to follow them.
The first one, is "add the first equation with the third one, this will eliminate an x-term". So I assume that, in my context, this will eliminate at least one term when I try it.
Adding the first with the third one: $$9a+3b+c=0$$ $$a-b+c=12$$ I get: $$10a-2b+2c$$ Aw... No term was removed. So something's not well.
Either my system is wrong or I am not following the instructions well. If you want to know where my system comes from, it is from the following question:
Determine the quadratic function such that $f(3) = 0$, $f(-5) = 0$ and $f(-1)=12$.
If I'm not mistaken, this involves solving the system I got above.
Can you tell me what did I do wrong following those instructions? I'm not really looking for the solution - instead, I'd prefer to understand how to do this.