First we can take out a common factor of 2:
---------------------------------------
We learn the principle of factorising the
difference of two squares. Here
is why it works:
A²-B² = (A-B)(A+B)
Proof: (A-B)(A+B) = A²+AB-AB-B² = A²-B²
So we memorise:
A²-B² is factorized as (A-B)(A+B)
--------------------------------------
Now back to this:
Since 4=2², we can rewrite that as
and again as
Since we have memorized that
A²-B² is factorised as (A-B)(A+B)
We can substitute 2x for A and y for B and get that
is factorised as
Edwin