It's: x^2,5 - 20x^0,5 + 19 = 0
You might need to re-check the above equation.
Is the following correct for f(x), which was perhaps given in an earlier part of the question?
f(x)=xx2−4
I would start with the substitution a=b² where b>0. This gives
b5−20b+19=0
can you spot any values of b that satisfy? If so then you've found a factor
Yeah, I've tried that. It's obvious that 1 is one of the values, but how do you find the other one?