Using the given zero, find one other zero of f(x). 2 - 4i is a zero of f(x).= x4 - 4x3 + 21x2 - 4x + 20 a.1 + i b.1 c.1 - i d.2 + 4i

2 + 4i

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

Factoring out (x² -4x +20) from f(x) gives (x² +1). Its roots are ±i, so are not on the list of answer choices.