PreCalc

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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 -

    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 -

    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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