Answer:
2 + 4i
Explanation:
Complex roots of polynomials with real coefficients come in conjugate pairs. The conjugate of a complex number has the same real part, but an imaginary part with opposite sign. (It is sometimes indicated using an asterisk.)
(2 - 4i)* = 2 + 4i . . . . . . the other complex root of this conjugate pair
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Factoring out (x² -4x +20) from f(x) gives (x² +1). Its roots are ±i, so are not on the list of answer choices.
