Posted by **Barb** on Wednesday, September 22, 2010 at 10:27pm.

6.Given -2i is a root, determine all other roots of x^4-10x^3+42x^2-88x+80.

A. x= +/- 4, 2i

B.x= -2, +/- 4i

C.x= -4, +/- 2

D.x= -4, 2i

E.x= +/- 4, 2

Please help, I do not understand where to begin.

- PreCalc -
**bobpursley**, Wednesday, September 22, 2010 at 10:30pm
If -2i is a root,then+2i is a root.

so then it is either A or D. Since you know there are 4 roots in a fourth degree polynomial, D does not offer two roots, so A has to be the answer.

- PreCalc -
**bobpursley**, Wednesday, September 22, 2010 at 10:35pm
Now that I look at A, I do not see how -4 can be a root.

checking

256+640+672+88*4+80 is not a root. Thatmeans neither A nor D is a root. Which means none of the answers are then right.

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