Answer:
y = x² -2x +5
Step-by-step explanation:
When a polynomial has q as a zero, it has (x-q) as a factor. Your polynomial has factors (x -(1-2i)) and (x -(1+2i)). The polynomial will be the product of these factors.
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y = (x -(1 -2i))(x -(1 +2i))
y = ((x -1) +2i)((x -1) -2i) = (x -1)² -(2i)² = x² -2x +1 -4(-1)
y = x² -2x +5
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Additional comments
i is the imaginary number √(-1), so i² = -1.
The two given roots differ only in the sign of their imaginary parts, so they are "conjugates" of each other. Complex roots of polynomials with real coefficients always come in conjugate pairs. (In some problems, you will be expected to supply the missing root of a conjugate pair.)
The expression for the product of the factors is simplified using the factoring for the difference of squares:
(a -b)(a +b) = a² -b² . . . . . . . here, we have a=(x-1); b=2i
