Solution:
Find the least common denominator (L.C.D ) of the expressions below

Concept:
We will factorize each of the expressions and then find the least common denominator of both of them
Step 1:
Factorize

To do this, we will have to look for two numbers that can be multiplied each other to give +4 and the same two numbers will add up to give +5
By try and error, we will have

From the above illustration, the two numbers to be used are +1 and +4
Replace the 5x with +x and +4x in the expression below

Step 2:
Factorize the expression below using the difference of two squares

The difference of the two squares involve

By applying the principle above, we will have

Note:
The Least Common Denominator will have everything from both - but not duplicated.
Therefore,
The least common denominator of (x² +5x +4 and (x² -16) is = (x + 4)(x - 4)(x -1 )