We will start with to simple equations:
(1)
and
(2)
Now, by inserting (2) into (1), we get:
(3)
After multiplication, eq. (3) yields:
(4)
Now let us clarify the structure of eq. (4) by shifting all terms including the number 3 on the left side, and all terms including the number 2 on the right side:
(5)
Eq. (5) may be written even more clearly by the use of brackets:
(6)
Now it is very easy to see, that indeed