Cho hai số phức <span class="MathJax_Preview" style="color: inherit; display: none;"></span><span id="MathJax-Element-1-Frame" class="mjx-chtml MathJax_CHTML" tabindex="0" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><mstyle mathsize="1.2em"><msub><mi>z</mi><mn>1</mn></msub><mo>=</mo><mn>2</mn><mo>−</mo><mn>4</mn><mi>i</mi></mstyle></math>" role="presentation" style="font-size: 127%; position: relative;"><span id="MJXc-Node-1" class="mjx-math" aria-hidden="true"><span id="MJXc-Node-2" class="mjx-mrow"><span id="MJXc-Node-3" class="mjx-mstyle"><span id="MJXc-Node-4" class="mjx-mrow" style="font-size: 120%;"><span id="MJXc-Node-5" class="mjx-msubsup"><span class="mjx-base" style="margin-right: -0.003em;"><span id="MJXc-Node-6" class="mjx-mi"><span class="mjx-char MJXc-TeX-math-I" style="padding-top: 0.199em; padding-bottom: 0.298em; padding-right: 0.003em;">z</span></span></span><span class="mjx-sub" style="font-size: 70.7%; vertical-align: -0.212em; padding-right: 0.071em;"><span id="MJXc-Node-7" class="mjx-mn" style=""><span class="mjx-char MJXc-TeX-main-R" style="padding-top: 0.396em; padding-bottom: 0.347em;">1</span></span></span></span><span id="MJXc-Node-8" class="mjx-mo MJXc-space3"><span class="mjx-char MJXc-TeX-main-R" style="padding-top: 0.101em; padding-bottom: 0.298em;">=</span></span><span id="MJXc-Node-9" class="mjx-mn MJXc-space3"><span class="mjx-char MJXc-TeX-main-R" style="padding-top: 0.396em; padding-bottom: 0.347em;">2</span></span><span id="MJXc-Node-10" class="mjx-mo MJXc-space2"><span class="mjx-char MJXc-TeX-main-R" style="padding-top: 0.298em; padding-bottom: 0.445em;">−</span></span><span id="MJXc-Node-11" class="mjx-mn MJXc-space2"><span class="mjx-char MJXc-TeX-main-R" style="padding-top: 0.396em; padding-bottom: 0.347em;">4</span></span><span id="MJXc-Node-12" class="mjx-mi"><span class="mjx-char MJXc-TeX-math-I" style="padding-top: 0.445em; padding-bottom: 0.298em;">i</span></span></span></span></span></span><span class="MJX_Assistive_MathML" role="presentation"><math xmlns="http://www.w3.org/1998/Math/MathML"><mstyle mathsize="1.2em"><msub><mi>z</mi><mn>1</mn></msub><mo>=</mo><mn>2</mn><mo>−</mo><mn>4</mn><mi>i</mi></mstyle></math></span></span><script type="math/tex" id="MathJax-Element-1">\large z_1= 2- 4i </script> và <span class="MathJax_Preview" style="color: inherit; display: none;"></span><span id="MathJax-Element-2-Frame" class="mjx-chtml MathJax_CHTML" tabindex="0" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><mstyle mathsize="1.2em"><msub><mi>z</mi><mn>2</mn></msub><mo>=</mo><mn>1</mn><mo>−</mo><mn>3</mn><mi>i</mi></mstyle></math>" role="presentation" style="font-size: 127%; position: relative;"><span id="MJXc-Node-13" class="mjx-math" aria-hidden="true"><span id="MJXc-Node-14" class="mjx-mrow"><span id="MJXc-Node-15" class="mjx-mstyle"><span id="MJXc-Node-16" class="mjx-mrow" style="font-size: 120%;"><span id="MJXc-Node-17" class="mjx-msubsup"><span class="mjx-base" style="margin-right: -0.003em;"><span id="MJXc-Node-18" class="mjx-mi"><span class="mjx-char MJXc-TeX-math-I" style="padding-top: 0.199em; padding-bottom: 0.298em; padding-right: 0.003em;">z</span></span></span><span class="mjx-sub" style="font-size: 70.7%; vertical-align: -0.212em; padding-right: 0.071em;"><span id="MJXc-Node-19" class="mjx-mn" style=""><span class="mjx-char MJXc-TeX-main-R" style="padding-top: 0.396em; padding-bottom: 0.347em;">2</span></span></span></span><span id="MJXc-Node-20" class="mjx-mo MJXc-space3"><span class="mjx-char MJXc-TeX-main-R" style="padding-top: 0.101em; padding-bottom: 0.298em;">=</span></span><span id="MJXc-Node-21" class="mjx-mn MJXc-space3"><span class="mjx-char MJXc-TeX-main-R" style="padding-top: 0.396em; padding-bottom: 0.347em;">1</span></span><span id="MJXc-Node-22" class="mjx-mo MJXc-space2"><span class="mjx-char MJXc-TeX-main-R" style="padding-top: 0.298em; padding-bottom: 0.445em;">−</span></span><span id="MJXc-Node-23" class="mjx-mn MJXc-space2"><span class="mjx-char MJXc-TeX-main-R" style="padding-top: 0.396em; padding-bottom: 0.347em;">3</span></span><span id="MJXc-Node-24" class="mjx-mi"><span class="mjx-char MJXc-TeX-math-I" style="padding-top: 0.445em; padding-bottom: 0.298em;">i</span></span></span></span></span></span><span class="MJX_Assistive_MathML" role="presentation"><math xmlns="http://www.w3.org/1998/Math/MathML"><mstyle mathsize="1.2em"><msub><mi>z</mi><mn>2</mn></msub><mo>=</mo><mn>1</mn><mo>−</mo><mn>3</mn><mi>i</mi></mstyle></math></span></span><script type="math/tex" id="MathJax-Element-2">\large z_2= 1- 3i</script>. Phần ảo c

Cho hai số phức $\large z_1= 2- 4i$ và $\large z_2= 1- 3i$ . Phần ảo c

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Tác giả: Thầy Tùng

Đăng ngày: 18 Aug 2022

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Lời giải chi tiết

Câu hỏi:

Cho hai số phức $\large z_1= 2- 4i$ và $\large z_2= 1- 3i$ . Phần ảo của số phức $\large z_1+ i.\bar{z_2}$ bằng

A. A. -5i
B. B. -3i
C. C. -3
D. D. -5

Đáp án án đúng là: C

Lời giải chi tiết:

Chọn C

Ta có: $\large z_1+ i.\bar{z_2} = 2- 4i + i(1+3i) = -1- 3i$

Vậy phần ảo của số phức $\large z_1+ i.\bar{z_2}$ là -3

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