SOLUTION: What cubic polynomial has roots -4 and 2i

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Question 1156705: What cubic polynomial has roots -4 and 2i
Answer by Boreal(15235) About Me  (Show Source):
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the third root is -2i, since complex numbers come in conjugates
(x+4)=0
x+2i=0
x-2i=0
multiply the second and third together and get x^2-4i^2 or x^2+4
multiply that by (x+4)
x^3+4x^2+4x+16
graph%28300%2C300%2C-10%2C10%2C-100%2C100%2Cx%5E3%2B4x%5E2%2B4x%2B16%29