Question

If one of the zeros of the cubic polynomial x3 + ax2 + bx + c is -1, then what will be the product of the other two zeros?

Answer 1

The product of the other two zeros is c

Explanation:

Let α, β and γ be the zeros of the polynomial x³ + ax² + bx + c. Since one of the zeros is -1, therefore let γ = -1. Hence:

sum of the roots = α + β + γ = -a

-1 + β + γ = -a

β + γ = -a + 1

αβ + αγ + βγ = b

-1(β) + (-1)γ + βγ = b

-β -γ + βγ = b

Also, the product of the zeros is equal to -c, hence:

αβγ = -c

-1(βγ) = -c

βγ = c

Hence the product of the other two zeros is c