For this case we have the following expression:

We follow the steps below:
We subtract 4x on both sides of the equation:

We subtract 10 from both sides of the equation:

Now, we must complete squares.
When we have an equation of the form:
, if we want to complete squares we must subtract c on both sides of the equation obtaining:

The square is completed by adding to both sides of the equation: 
So, we have left:

In the given expression we have:

And to complete the square we have:

Rewriting we have:

We factor the left side of the equation, that is, we look for two numbers that when added together result in -8 and when multiplied as a result 16. We have:

So, we have:

Answer:
The intermediate step is to complete squares

A common misconception in statistics is confusing correlation with causation. If two events are correlated, it merely means that they share the same behaviour over time, but it doesn't imply in any way that those event are related by a common cause, or even worse, that one implies the other.
You can find several (even humorous) counter examples online. For example, if you plot the number of reported pirates assault against the global temperature in the last years, you'll se that temperature is rising (unfortunately...) while pirates are almost disappearing.
One could observe this strong negative correlation and claim that hotter climate has solved the pirate issue. Of course this is a joke, but it explains why you shouldn't confuse correlation with causation.
Answer:
See proof below
Step-by-step explanation:
We will use properties of inequalities during the proof.
Let
. then we have that
. Hence, it makes sense to define the positive number delta as
(the inequality guarantees that these numbers are positive).
Intuitively, delta is the shortest distance from y to the endpoints of the interval. Now, we claim that
, and if we prove this, we are done. To prove it, let
, then
. First,
then
hence
On the other hand,
then
hence
. Combining the inequalities, we have that
, therefore
as required.
(2,4), (4,8), (3,6), (5,10) because they’re all ratios of 1:2