# If z^2 + αz + β = 0 has one root 1 − 2i, where α, β ∈ R. Find the value of α − β

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If $z^2+\alpha z+\beta=0$ has one root $1-2i,$ where $\alpha,\ \beta\in R$. Find the value of $\alpha-\beta$

(1) 12

(2) 10

(3) –7

(4) 7