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Câu hỏi: Cho hai số phức ${{z}_{1}}=1+2i$, ${{z}_{2}}=1-i$. Số phức $\dfrac{{{z}_{1}}}{{{z}_{2}}}$ là
A. $-\dfrac{1}{2}+\dfrac{3}{2}i$.
B. $\dfrac{1}{2}-\dfrac{3}{2}i$.
C. $-1+3i$.
D. $\dfrac{3}{2}-\dfrac{1}{2}i$.
A. $-\dfrac{1}{2}+\dfrac{3}{2}i$.
B. $\dfrac{1}{2}-\dfrac{3}{2}i$.
C. $-1+3i$.
D. $\dfrac{3}{2}-\dfrac{1}{2}i$.
Ta có: $\dfrac{{{z}_{1}}}{{{z}_{2}}}=\dfrac{1+2i}{1-i}=\dfrac{\left( 1+2i \right)\left( 1+i \right)}{\left( 1-i \right)\left( 1+i \right)}=\dfrac{-1+3i}{2}=-\dfrac{1}{2}+\dfrac{3}{2}i$.
Đáp án A.