Cho 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><script type="math/tex" id="MathJax-Element-1">\large ABC</script> có <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">B</span><span class="MJXp-mo" id="MJXp-Span-10" style="margin-left: 0.333em; margin-right: 0.333em;">=</span><span class="MJXp-mn" id="MJXp-Span-11">4</span><span class="MJXp-mi MJXp-italic" id="MJXp-Span-12">c</span><span class="MJXp-mi MJXp-italic" id="MJXp-Span-13">m</span></span></span></span><script type="math/tex" id="MathJax-Element-2">\large AB=4cm</script>, <span class="MathJax_Preview" style="color: inherit;"><span class="MJXp-math" id="MJXp-Span-14"><span class="MJXp-mstyle" id="MJXp-Span-15"><span class="MJXp-mi MJXp-italic" id="MJXp-Span-16">A</span><span class="MJXp-mi MJXp-italic" id="MJXp-Span-17">C</span><span class="MJXp-mo" id="MJXp-Span-18" style="margin-left: 0.333em; margin-right: 0.333em;">=</span><span class="MJXp-mn" id="MJXp-Span-19">5</span><span class="MJXp-mi MJXp-italic" id="MJXp-Span-20">c</span><span class="MJXp-mi MJXp-italic" id="MJXp-Span-21">m</span></span></span></span><script type="math/tex" id="MathJax-Element-3">\large AC=5cm</script>, $\large

Cho tam giác ABCAB=4cm, AC=5cm, $\large

4.8/5

Tác giả: Thầy Tùng

Đăng ngày: 18 Aug 2022

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Câu hỏi:

Cho tam giác ABCAB=4cm, AC=5cm, BC=6cm. Các đường phân giác BDCE cắt nhau ở I. Tỉ số diện tích của tam giác DIEABC

Đáp án án đúng là: A

Lời giải chi tiết:

Ta có: ADAB=DCBC (tính chất)

 AD4=DC6=AD+DC4+6=510=12

 AD=4.12=2, DC=6.12=3.

Suy ra:

 DIIB=DCCB=36=12DIDB=13;

 BEEA=BCAC=65BEBA=611;

 ADDC=23ADAC=25.

Suy ra SDIE=13SBDE, SDBE=611.SABD, SABD=25SABC

 SDIE=13.611.25=455SABC

Vậy SDIESABC=455