Step by step
The question
Question: find (f/g)(x) for f(x) = 5x − 10 and g(x) = x − 2.
(f/g)(x) means f of x divided by g of x.
We write it as a fraction: f on top, g at the bottom.
1 Put the rules in
Each rule goes in as one piece: (5x − 10)/(x − 2).
2 Simplify
The top: 5x − 10.
Every part can be divided by 5.
We take it out in front.
So the top is 5(x − 2).
Now the same bracket is on the top and the bottom.
(x − 2)/(x − 2) is 1.
Cross them out.
What is left: 5.
3 Find what x can't be
We can never divide by 0.
So the bottom, g of x, can never be 0.
Careful!
The crossed-out bracket was the bottom, g.
In the question, x = 2 still makes the bottom 0.
So it stays not allowed.
Which x makes x − 2 zero?
We solve x − 2 = 0.
4 Remove the − 2
We want x by itself.
The − 2 is in the way.
To remove − 2, we add 2.
We do it on both sides, so they stay equal.
− 2 and + 2 make zero.
Cross them out.
0 + 2 = 2.
So x = 2!
So (f/g)(x) = 5, with x ≠ 2.
5 Check
Let's check with a number: x = 1.
f of 1 is −5, g of 1 is −1.
Divided: 5.
Our answer gives 5 too.
It works!
Let's look back.
First: put the rules in.
Then: simplify.
Then: find what x can't be.
Then: remove the − 2.
Last: check.