Answer:
a =1 and a=4.
Step-by-step explanation:
The function is

If we want f(x) to be continuous the denominator needs to be different to 0, otherwise f(x) will be indeterminate.
Now, for a a positive real we have that
will annulate the denominator, i.e
. But, if a = 1 we have:

so, the value
won't annulate the denominator.
Now, for a = 4 we have:

so, the value
won't annulate the denominator.
In conclusion, for a=1 or a=1, the function will be continuos for all real numbers, since the denominator will never be 0.