15. One of the roots of the equation x3 7x2 + 25x 39 = 0 is 3. What are the other 2 roots of this equation?

A. 1 and 5

B. 1 and 13

C. 2(17)1/2 and 2+(17)1/2

D. 2 3i and 2 + 3i

E. 3 2i and 3 + 2i

 

Solution: The answer is D

Since 3 is a root, then (x-3) is a factor of x3 7x2 + 25x 39. Use the method of long division to find another factor, as follows:

Since x2 4x + 13 is not factorable, use the quadratic formula to find the other two roots.