Tìm số tự nhiên n thỏa mãn <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="1.44em"><msubsup><mi>C</mi><mrow class="MJX-TeXAtom-ORD"><mi>n</mi><mo>+</mo><mn>5</mn></mrow><mrow class="MJX-TeXAtom-ORD"><mi>n</mi></mrow></msubsup><mo>=</mo><mn>5</mn><msubsup><mi>A</mi><mrow class="MJX-TeXAtom-ORD"><mi>n</mi><mo>+</mo><mn>3</mn></mrow><mrow class="MJX-TeXAtom-ORD"><mn>3</mn></mrow></msubsup></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: 144%;"><span id="MJXc-Node-5" class="mjx-msubsup"><span class="mjx-base" style="margin-right: -0.045em;"><span id="MJXc-Node-6" class="mjx-mi"><span class="mjx-char MJXc-TeX-math-I" style="padding-top: 0.495em; padding-bottom: 0.298em; padding-right: 0.045em;">C</span></span></span><span class="mjx-stack" style="vertical-align: -0.315em;"><span class="mjx-sup" style="font-size: 70.7%; padding-bottom: 0.255em; padding-left: 0.153em; padding-right: 0.071em;"><span id="MJXc-Node-12" class="mjx-texatom" style=""><span id="MJXc-Node-13" class="mjx-mrow"><span id="MJXc-Node-14" class="mjx-mi"><span class="mjx-char MJXc-TeX-math-I" style="padding-top: 0.199em; padding-bottom: 0.298em;">n</span></span></span></span></span><span class="mjx-sub" style="font-size: 70.7%; padding-right: 0.071em;"><span id="MJXc-Node-7" class="mjx-texatom" style=""><span id="MJXc-Node-8" class="mjx-mrow"><span id="MJXc-Node-9" class="mjx-mi"><span class="mjx-char MJXc-TeX-math-I" style="padding-top: 0.199em; padding-bottom: 0.298em;">n</span></span><span id="MJXc-Node-10" class="mjx-mo"><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"><span class="mjx-char MJXc-TeX-main-R" style="padding-top: 0.396em; padding-bottom: 0.347em;">5</span></span></span></span></span></span></span><span id="MJXc-Node-15" 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-16" class="mjx-mn MJXc-space3"><span class="mjx-char MJXc-TeX-main-R" style="padding-top: 0.396em; padding-bottom: 0.347em;">5</span></span><span id="MJXc-Node-17" class="mjx-msubsup"><span class="mjx-base"><span id="MJXc-Node-18" class="mjx-mi"><span class="mjx-char MJXc-TeX-math-I" style="padding-top: 0.495em; padding-bottom: 0.298em;">A</span></span></span><span class="mjx-stack" style="vertical-align: -0.314em;"><span class="mjx-sup" style="font-size: 70.7%; padding-bottom: 0.255em; padding-left: 0px; padding-right: 0.071em;"><span id="MJXc-Node-24" class="mjx-texatom" style=""><span id="MJXc-Node-25" class="mjx-mrow"><span id="MJXc-Node-26" class="mjx-mn"><span class="mjx-char MJXc-TeX-main-R" style="padding-top: 0.396em; padding-bottom: 0.347em;">3</span></span></span></span></span><span class="mjx-sub" style="font-size: 70.7%; padding-right: 0.071em;"><span id="MJXc-Node-19" class="mjx-texatom" style=""><span id="MJXc-Node-20" class="mjx-mrow"><span id="MJXc-Node-21" class="mjx-mi"><span class="mjx-char MJXc-TeX-math-I" style="padding-top: 0.199em; padding-bottom: 0.298em;">n</span></span><span id="MJXc-Node-22" class="mjx-mo"><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"><span class="mjx-char MJXc-TeX-main-R" style="padding-top: 0.396em; padding-bottom: 0.347em;">3</span></span></span></span></span></span></span></span></span></span></span><span class="MJX_Assistive_MathML" role="presentation"><math xmlns="http://www.w3.org/1998/Math/MathML"><mstyle mathsize="1.44em"><msubsup><mi>C</mi><mrow class="MJX-TeXAtom-ORD"><mi>n</mi><mo>+</mo><mn>5</mn></mrow><mrow class="MJX-TeXAtom-ORD"><mi>n</mi></mrow></msubsup><mo>=</mo><mn>5</mn><msubsup><mi>A</mi><mrow class="MJX-TeXAtom-ORD"><mi>n</mi><mo>+</mo><mn>3</mn></mrow><mrow class="MJX-TeXAtom-ORD"><mn>3</mn></mrow></msubsup></mstyle></math></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 Cn+5n=5An+33 n=20 n

4.3/5

Tác giả: Thầy Tùng

Đăng ngày: 18 Aug 2022

Lưu về Facebook:

Câu hỏi:

Tìm số tự nhiên n thỏa mãn Cn+5n=5An+33

Đáp án án đúng là: A

Lời giải chi tiết:

Cn+5n=5An+33

(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