Answer:
1/2
Explanation:
The Rational Root Theorem says that any rational root has
1. a numerator that is a factor of the constant term
2. a denominator that is a factor of the leading coefficient (that's attached to the highest-power term)
Numerator:

Denominator:

That means there are only two possible rational roots:

Try them both by plugging them into the polynomial.

Aha! The negative one-half value does not produce 0