Cho cấp số nhân <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"><mo stretchy="false">(</mo><msub><mi>u</mi><mi>n</mi></msub><mo stretchy="false">)</mo></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-mo"><span class="mjx-char MJXc-TeX-main-R" style="padding-top: 0.445em; padding-bottom: 0.593em;">(</span></span><span id="MJXc-Node-6" class="mjx-msubsup"><span class="mjx-base"><span id="MJXc-Node-7" class="mjx-mi"><span class="mjx-char MJXc-TeX-math-I" style="padding-top: 0.199em; padding-bottom: 0.298em;">u</span></span></span><span class="mjx-sub" style="font-size: 70.7%; vertical-align: -0.212em; padding-right: 0.071em;"><span id="MJXc-Node-8" class="mjx-mi" style=""><span class="mjx-char MJXc-TeX-math-I" style="padding-top: 0.199em; padding-bottom: 0.298em;">n</span></span></span></span><span id="MJXc-Node-9" class="mjx-mo"><span class="mjx-char MJXc-TeX-main-R" style="padding-top: 0.445em; padding-bottom: 0.593em;">)</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"><mo stretchy="false">(</mo><msub><mi>u</mi><mi>n</mi></msub><mo stretchy="false">)</mo></mstyle></math></span></span><script type="math/tex" id="MathJax-Element-1">\large (u_n)</script>, biết <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>u</mi><mn>1</mn></msub><mo>=</mo><mn>1</mn></mstyle></math>" role="presentation" style="font-size: 127%; position: relative;"><span id="MJXc-Node-10" class="mjx-math" aria-hidden="true"><span id="MJXc-Node-11" class="mjx-mrow"><span id="MJXc-Node-12" class="mjx-mstyle"><span id="MJXc-Node-13" class="mjx-mrow" style="font-size: 120%;"><span id="MJXc-Node-14" class="mjx-msubsup"><span class="mjx-base"><span id="MJXc-Node-15" class="mjx-mi"><span class="mjx-char MJXc-TeX-math-I" style="padding-top: 0.199em; padding-bottom: 0.298em;">u</span></span></span><span class="mjx-sub" style="font-size: 70.7%; vertical-align: -0.212em; padding-right: 0.071em;"><span id="MJXc-Node-16" 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-17" 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-18" 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></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>u</mi><mn>1</mn></msub><mo>=</mo><mn>1</mn></mstyle></math></span></span><script type="math/tex" id="MathJax-Element-2">\large u_1= 1</script> và $\large u_4 =

Cho cấp số nhân $\large (u_n)$ , biết $\large u_1= 1$ và $\large u_4 =

4.5/5

Tác giả: Thầy Tùng

Đăng ngày: 18 Aug 2022

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Lời giải chi tiết

Câu hỏi:

Cho cấp số nhân $\large (u_n)$ , biết $\large u_1= 1$ và $\large u_4 = 8$ . Công bội của cấp số nhân đã cho bằng

A. 1
B. 2
C. 3
D. -2

Đáp án án đúng là: A

Lời giải chi tiết:

Chọn B

$\large u_4 = u_1.q^3\Rightarrow q^3 = \dfrac{u_4}{u_1} = 8\Rightarrow q = 2$

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