Answer:
None.
Step-by-step explanation:
The only possible restriction in the rational expression [tex]\frac{am^2+4m}{a^2+4}[/tex] can originate in its denominator being zero for some values of a. However, since the denominator in this case (a^2+4) is always positive (and larger or equal to 4) for all values, no restrictions on the variable a exist.
