Cho cấp số cộng <span class="MathJax_Preview" style="color: inherit;"><span class="MJXp-math" id="MJXp-Span-1"><span class="MJXp-mstyle" id="MJXp-Span-2"><span class="MJXp-mo" id="MJXp-Span-3" style="margin-left: 0em; margin-right: 0em;">(</span><span class="MJXp-msubsup" id="MJXp-Span-4"><span class="MJXp-mi MJXp-italic" id="MJXp-Span-5" style="margin-right: 0.05em;">u</span><span class="MJXp-mi MJXp-italic MJXp-script" id="MJXp-Span-6" style="vertical-align: -0.4em;">n</span></span><span class="MJXp-mo" id="MJXp-Span-7" style="margin-left: 0em; margin-right: 0em;">)</span></span></span></span><span id="MathJax-Element-1-Frame" class="mjx-chtml MathJax_CHTML MJXc-processed" tabindex="0" style="font-size: 127%;"><span id="MJXc-Node-1" class="mjx-math"><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: 144%;"><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><script type="math/tex" id="MathJax-Element-1">\Large (u_n)</script> có công sai <span class="MathJax_Preview" style="color: inherit;"><span class="MJXp-math" id="MJXp-Span-8"><span class="MJXp-mstyle" id="MJXp-Span-9"><span class="MJXp-mi MJXp-italic" id="MJXp-Span-10">d</span><span class="MJXp-mo" id="MJXp-Span-11" style="margin-left: 0.333em; margin-right: 0.333em;">></span><span class="MJXp-mn" id="MJXp-Span-12">0</span></span></span></span><span id="MathJax-Element-2-Frame" class="mjx-chtml MathJax_CHTML MJXc-processed" tabindex="0" style="font-size: 127%;"><span id="MJXc-Node-10" class="mjx-math"><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: 144%;"><span id="MJXc-Node-14" class="mjx-mi"><span class="mjx-char MJXc-TeX-math-I" style="padding-top: 0.495em; padding-bottom: 0.298em; padding-right: 0.003em;">d</span></span><span id="MJXc-Node-15" class="mjx-mo MJXc-space3"><span class="mjx-char MJXc-TeX-main-R" style="padding-top: 0.249em; padding-bottom: 0.396em;">></span></span><span id="MJXc-Node-16" class="mjx-mn MJXc-space3"><span class="mjx-char MJXc-TeX-main-R" style="padding-top: 0.396em; padding-bottom: 0.347em;">0</span></span></span></span></span></span></span><script type="math/tex" id="MathJax-Element-2">\Large d > 0</script>; $\Large \le

Cho cấp số cộng (un)(un) có công sai d>0d>0; $\Large \le

4.8/5

Tác giả: Thầy Tùng

Đăng ngày: 18 Aug 2022

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Câu hỏi:

Cho cấp số cộng (un)(un) có công sai d>0d>0; {u31+u34=11u231+u234=101. Hãy tìm số hạng tổng quát của cấp số cộng đó.

Đáp án án đúng là: C

Lời giải chi tiết:

Ta có:

{u31+u34=11u231+u234=101

{u34=11u31u231+(11u31)2=101

{u31=1u34=10 hoặc {u31=10u34=1

{u1=89d=3 hoặc {u1=100d=3

{u1=89d=3 (d>0)

un=89+(n1)3=3n92.

Chọn C.