Answer:
-1/2
Step-by-step explanation:
Zeros of a polynomial function are its x-intercepts, the values of x that make the polynomial zero. Each zero x=p corresponds to a linear factor (x-p) of the polynomial.
Monic polynomial
A monic polynomial is one that has a leading coefficient of 1. For a monic polynomial of degree n, the coefficient of the term of degree n-1 is the opposite of the sum of all of the zeros. The constant term of any odd-degree monic polynomial is the opposite of the product of the zeros.
The given polynomial can be made monic by dividing by its leading coefficient:
(2x^3 -x^2 -5x -2)/2 = x^3 -(1/2)x^2 -(5/2)x -1
Sum of zeros
The given polynomial has degree 3, so we're interested in the coefficient of the x^2 term. That coefficient is -1/2, so the sum of zeros will be ...
sum of zeros = -(-1/2) = 1/2
If z represents the third zero, then we have the sum ...
1/2 = -1 +2 +z
z = -1/2 . . . . . . subtract 1 from both sides
The third zero is -1/2.
Product of zeros
The given polynomial is of odd degree, so the product of the zeros is the opposite of the constant.
(-1)(2)(z) = -(-1)
z = 1/(-2) = -1/2 . . . . . divide by the coefficient of z
The third zero is -1/2.
Graph
Of course, a graph will show all of the (real) zeros. The attached graph from a graphing calculator shows the third zero is -1/2.
