Answer:
x^2 - 10x + 41
Explanation:
since this is a quadratic equation with rational coefficients, the other root must be (5-4i)
now we have (x-(5+4i))(x-(5-4i))
which expands to (x^2) - x(5-4i) -x(5+4i) + (5+4i)(5-4i)
which simplifies to x^2 - 10x + 41
note: (5+4i)(5-4i) = 25 - (-16) = 41