Tam giác <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">A</span><span class="MJXp-mi MJXp-italic" id="MJXp-Span-4">B</span><span class="MJXp-mi MJXp-italic" id="MJXp-Span-5">C</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: 120%;"><span id="MJXc-Node-5" class="mjx-mi"><span class="mjx-char MJXc-TeX-math-I" style="padding-top: 0.495em; padding-bottom: 0.298em;">A</span></span><span id="MJXc-Node-6" class="mjx-mi"><span class="mjx-char MJXc-TeX-math-I" style="padding-top: 0.445em; padding-bottom: 0.298em;">B</span></span><span id="MJXc-Node-7" 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></span></span></span><script type="math/tex" id="MathJax-Element-1">\large ABC</script> có hai trung tuyến <span class="MathJax_Preview" style="color: inherit;"><span class="MJXp-math" id="MJXp-Span-6"><span class="MJXp-mstyle" id="MJXp-Span-7"><span class="MJXp-mi MJXp-italic" id="MJXp-Span-8">A</span><span class="MJXp-mi MJXp-italic" id="MJXp-Span-9">M</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-8" class="mjx-math"><span id="MJXc-Node-9" class="mjx-mrow"><span id="MJXc-Node-10" class="mjx-mstyle"><span id="MJXc-Node-11" class="mjx-mrow" style="font-size: 120%;"><span id="MJXc-Node-12" class="mjx-mi"><span class="mjx-char MJXc-TeX-math-I" style="padding-top: 0.495em; padding-bottom: 0.298em;">A</span></span><span id="MJXc-Node-13" class="mjx-mi"><span class="mjx-char MJXc-TeX-math-I" style="padding-top: 0.445em; padding-bottom: 0.298em; padding-right: 0.081em;">M</span></span></span></span></span></span></span><script type="math/tex" id="MathJax-Element-2">\large AM</script> và <span class="MathJax_Preview" style="color: inherit;"><span class="MJXp-math" id="MJXp-Span-10"><span class="MJXp-mstyle" id="MJXp-Span-11"><span class="MJXp-mi MJXp-italic" id="MJXp-Span-12">B</span><span class="MJXp-mi MJXp-italic" id="MJXp-Span-13">N</span></span></span></span><span id="MathJax-Element-3-Frame" class="mjx-chtml MathJax_CHTML MJXc-processed" tabindex="0" style="font-size: 127%;"><span id="MJXc-Node-14" class="mjx-math"><span id="MJXc-Node-15" class="mjx-mrow"><span id="MJXc-Node-16" class="mjx-mstyle"><span id="MJXc-Node-17" class="mjx-mrow" style="font-size: 120%;"><span id="MJXc-Node-18" class="mjx-mi"><span class="mjx-char MJXc-TeX-math-I" style="padding-top: 0.445em; padding-bottom: 0.298em;">B</span></span><span id="MJXc-Node-19" class="mjx-mi"><span class="mjx-char MJXc-TeX-math-I" style="padding-top: 0.445em; padding-bottom: 0.298em; padding-right: 0.085em;">N</span></span></span></span></span></span></span><script type="math/tex" id="MathJax-Element-3">\large BN</script> vu

Tam giác ABCABC có hai trung tuyến AMAMBNBN vu

4.6/5

Tác giả: Thầy Tùng

Đăng ngày: 18 Aug 2022

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Câu hỏi:

Tam giác ABCABC có hai trung tuyến AMAMBNBN vuông góc với nhau. Hãy tính diện tích tam giác đó theo hai cạnh AMAMBNBN.

 

Đáp án án đúng là: D

Lời giải chi tiết:

Ta có ABMNABMN là tứ giác có hai đường chéo AMAMBNBN vuông góc nên có diện tích là: SABMN=12AB.MNSABMN=12AB.MN

Xét tam giác ΔABCΔABCΔCNMΔCNM có:

 ˆCˆC chung

 CNCA=CMCB=12CNCA=CMCB=12

 ΔCABΔCNM(c.g.c)ΔCABΔCNM(c.g.c) theo tỉ số đồng dạng k=12

 SCNMSCAB=(12)2=14SABMNSABC=SABCSCNMSABC=34SABC=43SABMN=43.12AB.MN=23AB.MN