<h2>
2e - 3f = 4</h2><h2>
2e - 5f = 8</h2><h2 />
To solve this system of equations by addition, our first goal is to cancel
out one of the variables by adding the two equations together.
However, before we add, we need to cancel out a variable.
I would choose to cancel out the e's.
To do this, we need a 2e and a -2e and
here we have a 2e in both equations.
If we multiply the second equation by -1 however,
that will give us the -2e we are looking for.
So we have (-1)(2e - 3f) = (4)(-1).
So rewriting both equations, our first equation stays the same
but our second equation becomes -2e + 3f = -4.
Notice that every term in the second
equation has been multiplied by -1.
2e - 3f = 4
-2e + 5f = -8
Now when we add the equations together,
the e's cancel and we have 2f = -4 so f = -2.
To find e, plug -2 back in for f in the
first equation to get 2e - 3(-2) = 4.
Solving from here, e = -1.
Note that <em>e</em> comes before <em>f</em> in our final answer, (-1, -2).
To determine which variable should go first
in your answer, use alphabetical order.
