Question

Two roots of a 3-degree polynomial equation are 5 and -5. Which of the following cannot be the third root of the equation?

Answer 1

Answer:

5i and -5i

Step-by-step explanation:

Both of these would have to be in the equation for either of them to work, and as the problem already told us that there is only a 3rd root, neither will be our answer.

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Answer 2

Answer:

5i and -5i

Step-by-step explanation:

Imaginary roots come in pairs, so the third root must be a real number.  Therefore, neither 5i nor -5i can be the third root.