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# If x = 3i is a zero of P(x ) = x4 - 2x3 + x2 - 18x - 72 , then another zero must be x = 2?

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- Dr DLv 71 decade agoFavorite Answer
x = 3i works.

x = 2 does not work.

There will also be zero at x = -3i

P can be factorized as follows:

P(x) = (x^2 + 9) * (x^2 - 2x - 8)

= (x^2 + 9) * (x-4)*(x+2)

The other roots are x = -2 and +4

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