PreCalc
posted by Barb .
6.Given 2i is a root, determine all other roots of x^410x^3+42x^288x+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.

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. 
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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