Tính tổng <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-mi MJXp-italic" id="MJXp-Span-3">S</span><span class="MJXp-mo" id="MJXp-Span-4" style="margin-left: 0.333em; margin-right: 0.333em;">=</span><span class="MJXp-mo" id="MJXp-Span-5" style="margin-left: 0.267em; margin-right: 0.267em;">−</span><span class="MJXp-mn" id="MJXp-Span-6">2</span><span class="MJXp-mo" id="MJXp-Span-7" style="margin-left: 0.267em; margin-right: 0.267em;">+</span><span class="MJXp-mn" id="MJXp-Span-8">4</span><span class="MJXp-mo" id="MJXp-Span-9" style="margin-left: 0.267em; margin-right: 0.267em;">−</span><span class="MJXp-mn" id="MJXp-Span-10">8</span><span class="MJXp-mo" id="MJXp-Span-11" style="margin-left: 0.267em; margin-right: 0.267em;">+</span><span class="MJXp-mn" id="MJXp-Span-12">16</span><span class="MJXp-mo" id="MJXp-Span-13" style="margin-left: 0.267em; margin-right: 0.267em;">−</span><span class="MJXp-mn" id="MJXp-Span-14">32</span><span class="MJXp-mo" id="MJXp-Span-15" style="margin-left: 0.267em; margin-right: 0.267em;">+</span><span class="MJXp-mn" id="MJXp-Span-16">64</span><span class="MJXp-mo" id="MJXp-Span-17" style="margin-left: 0.267em; margin-right: 0.267em;">−</span><span class="MJXp-mo" id="MJXp-Span-18" style="margin-left: 0em; margin-right: 0.222em;">.</span><span class="MJXp-mo" id="MJXp-Span-19" style="margin-left: 0em; margin-right: 0.222em;">.</span><span class="MJXp-mo" id="MJXp-Span-20" style="margin-left: 0.267em; margin-right: 0.267em;">+</span><span class="MJXp-mo" id="MJXp-Span-21" style="margin-left: 0em; margin-right: 0em;">(</span><span class="MJXp-mo" id="MJXp-Span-22" style="margin-left: 0.267em; margin-right: 0.267em;">−</span><span class="MJXp-mn" id="MJXp-Span-23">2</span><span class="MJXp-msubsup" id="MJXp-Span-24"><span class="MJXp-mo" id="MJXp-Span-25" style="margin-left: 0em; margin-right: 0.05em;">)</span><span class="MJXp-mrow MJXp-script" id="MJXp-Span-26" style="vertical-align: 0.5em;"><span class="MJXp-mi MJXp-italic" id="MJXp-Span-27">n</span><span class="MJXp-mo" id="MJXp-Span-28">−</span><span class="MJXp-mn" id="MJXp-Span-29">1</span></span></span><span class="MJXp-mo" id="MJXp-Span-30" style="margin-left: 0.267em; margin-right: 0.267em;">+</span><span class="MJXp-mo" id="MJXp-Span-31" style="margin-left: 0em; margin-right: 0em;">(</span><span class="MJXp-mo" id="MJXp-Span-32" style="margin-left: 0.267em; margin-right: 0.267em;">−</span><span class="MJXp-mn" id="MJXp-Span-33">2</span><span class="MJXp-msubsup" id="MJXp-Span-34"><span class="MJXp-mo" id="MJXp-Span-35" style="margin-left: 0em; margin-right: 0.05em;">)</span><span class="MJXp-mi MJXp-italic MJXp-script" id="MJXp-Span-36" style="vertical-align: 0.5em;">n</span></span></span></span></span><script type="math/tex" id="MathJax-Element-1">\large S = -2+4-8+16-32+64-..+ (-2)^{n-1} + (-2)^n</script> với $\l

Tính tổng S=2+48+1632+64..+(2)n1+(2)n với $\l

4.1/5

Tác giả: Thầy Tùng

Đăng ngày: 18 Aug 2022

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Câu hỏi:

Tính tổng S=2+48+1632+64..+(2)n1+(2)n với n1,nN

Đáp án án đúng là: D

Lời giải chi tiết:

Chọn D

Các số hạng 2;4;8;16;32;64;...;(2)n1;(2)n trong tổng S gồm có n số hạng theo thứ tự đó lập thành cấp số nhân có u1=2;q=2. Vậy

S=Sn=u1.1qn1q=2.1(2)n1(2)=2.1(2)n3