what is the non-permissible value of (5p^2+4)/(p^2-5p+4)

Answer 1

I suppose if the denominator were zero it could be called "non-permissible".
(p^2-5p+4) = (p-4)(p-1) = 0
when is p-4 = 0 and when is p-1 = 0 ?