Tìm số tự nhiên n thỏa mãn <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-msubsup" id="MJXp-Span-3"><span class="MJXp-mi MJXp-italic" id="MJXp-Span-4" style="margin-right: 0.05em;">C</span><span class="MJXp-script-box" style="height: 1.86em; vertical-align: -0.64em;"><span class=" MJXp-script"><span><span style="margin-bottom: -0.25em;"><span class="MJXp-mrow" id="MJXp-Span-9"><span class="MJXp-mi MJXp-italic" id="MJXp-Span-10">n</span></span></span></span></span><span class=" MJXp-script"><span><span style="margin-top: -0.85em;"><span class="MJXp-mrow" id="MJXp-Span-5"><span class="MJXp-mi MJXp-italic" id="MJXp-Span-6">n</span><span class="MJXp-mo" id="MJXp-Span-7">+</span><span class="MJXp-mn" id="MJXp-Span-8">5</span></span></span></span></span></span></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">5</span><span class="MJXp-msubsup" id="MJXp-Span-13"><span class="MJXp-mi MJXp-italic" id="MJXp-Span-14" style="margin-right: 0.05em;">A</span><span class="MJXp-script-box" style="height: 1.86em; vertical-align: -0.64em;"><span class=" MJXp-script"><span><span style="margin-bottom: -0.25em;"><span class="MJXp-mrow" id="MJXp-Span-19"><span class="MJXp-mn" id="MJXp-Span-20">3</span></span></span></span></span><span class=" MJXp-script"><span><span style="margin-top: -0.85em;"><span class="MJXp-mrow" id="MJXp-Span-15"><span class="MJXp-mi MJXp-italic" id="MJXp-Span-16">n</span><span class="MJXp-mo" id="MJXp-Span-17">+</span><span class="MJXp-mn" id="MJXp-Span-18">3</span></span></span></span></span></span></span></span></span></span><script type="math/tex" id="MathJax-Element-1">\Large C _{n+5}^{n}=5 A _{n+3}^{3}</script> n=20 n

Tìm số tự nhiên n thỏa mãn Cnn+5=5A3n+3 n=20 n

4.3/5

Tác giả: Thầy Tùng

Đăng ngày: 18 Aug 2022

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Câu hỏi:

Tìm số tự nhiên n thỏa mãn Cnn+5=5A3n+3

Đáp án án đúng là: A

Lời giải chi tiết:

Cnn+5=5A3n+3

(n+5)(n+4)(n+3)(n+2)(n+1)5!=5(n+3)(n+2)(n+1)

(n+5)(n+4)=55!

n=20

Chọn đáp án A