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Quoc Tran Anh Le
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Hà Quang Minh
25 tháng 9 2023 lúc 16:47

Áp dụng định lí cosin trong tam giác ABC, ta có:

\(\begin{array}{l}{c^2} = {b^2} + {a^2} - 2ab\cos C\\ \Leftrightarrow {c^2} = 26,{4^2} + 49,{4^2} - 2.26,4.49,4\cos {47^ \circ }20'\\ \Rightarrow c \approx 37\end{array}\)

Áp dụng định lí sin, ta có: \(\frac{a}{{\sin A}} = \frac{b}{{\sin B}} = \frac{c}{{\sin C}}\)

\(\begin{array}{l} \Leftrightarrow \frac{{49,4}}{{\sin A}} = \frac{{26,4}}{{\sin B}} = \frac{{37}}{{\sin {{47}^ \circ }20'}}\\ \Rightarrow \sin A = \frac{{49,4.\sin {{47}^ \circ }20'}}{{37}} \approx 0,982 \Rightarrow \widehat A \approx {79^ \circ }\\ \Rightarrow \widehat B \approx {180^ \circ } - {79^ \circ } - {47^ \circ }20' = {53^ \circ }40'\end{array}\)

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Tiếng anh123456
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Nguyễn Lê Phước Thịnh
14 tháng 10 2023 lúc 11:02

Xét ΔABC có 

\(cosC=\dfrac{CA^2+CB^2-AB^2}{2\cdot CA\cdot CB}\)

=>\(\dfrac{26.4^2+49.4^2-AB^2}{2\cdot26.4\cdot49.4}=cos\left(47^020'\right)\)

=>\(3137.32-AB^2=2608.32\cdot cos\left(47^020'\right)\)

=>\(AB=\sqrt{3137.32-2608.32\cdot cos47^020'}\simeq37\left(cm\right)\)

Xét ΔABC có \(\dfrac{AB}{sinC}=\dfrac{AC}{sinB}=\dfrac{BC}{sinA}\)

=>\(\dfrac{37}{sin47^020'}=\dfrac{26.4}{sinB}=\dfrac{49.4}{sinA}\)

=>\(\left\{{}\begin{matrix}sinB\simeq0.52\\sinA\simeq0.98\end{matrix}\right.\Leftrightarrow\widehat{B}\simeq31^019'\)

\(\widehat{A}=180^0-31^019'-47^020'=101^021'\)

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Minh Hiếu
14 tháng 10 2023 lúc 11:04

\(c=\sqrt{a^2+b^2-2.a.b.cosC}\)

\(=\sqrt{49,4^2+26,4^2-2.26,4.49,4.cos47^o20'}\simeq37\)

Ta có:

\(cosA=\dfrac{b^2+c^2-a^2}{2bc}=\dfrac{\left(26,4\right)^2+37^2-\left(49,4\right)^2}{2.26,4.37}\simeq-0,2\)

\(\Rightarrow\widehat{A}\simeq101,5^o\)

\(\Rightarrow\widehat{B}=180^o-101,5^o-47,3^o=31,2^o\)

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Áp dụng định lí côsin ta có:

c2 = a2 + b2 - 2ab.cos C = 49,42 + 26,42 - 2 . 49,4 . 26,4 . cos

47°20' ≈ 1 369,58

 c ~ 37

Áp dụng hệ quả của định lí côsin ta có:

Cos A = \(\dfrac{b^2+c^2-a^2}{^{2bc}}\) \(=\) \(\dfrac{26,4^2+37^2-49,4^2}{2.26,4.37}\) \(\rightarrow\) _0,19

\(\rightarrow\) \(Â\) ~ 101°3'

Khi đó B = 180° - \((Â+C)\) \(\rightarrow\)31°37’.

 

 

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dsfdsf
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Trịnh Việt Dũng
15 tháng 6 2022 lúc 20:31

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Đỗ Vũ Nhật Anh
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Duy Nghĩa Hoàng
15 tháng 11 2021 lúc 21:58

Giống mình làm

 

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Bà HOÀng Thả ThÍnh
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Dương Mạnh Quyết
21 tháng 12 2021 lúc 10:21

bài 2:

ta có: AB<AC<BC(Vì 3cm<4cm<5cm)

=> góc C>góc A> góc B (Các cạnh và góc đồi diện trong tam giác)

Bài 3:

*Xét tam giác ABC, có:

       góc A+góc B+góc c= 180 độ( tổng 3 góc 1 tam giác)

hay góc A+60 độ +40 độ=180độ

  => góc A= 180 độ-60 độ-40 độ.

  => góc A=80 độ

Ta có: góc A>góc B>góc C(vì 80 độ>60 độ>40 độ)

        => BC>AC>AB( Các cạnh và góc đối diện trong tam giác)

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 Khách vãng lai đã xóa
Lưu Nguyễn Hà An
15 tháng 2 2022 lúc 9:04

bài 2:

ta có: AB <AC <BC (Vì 3cm <4cm <5cm)

=> góc C>góc A> góc B (Các cạnh và góc đồi diện trong tam giác)

Bài 3:

*Xét tam giác ABC, có:

       góc A+góc B+góc c= 180 độ( tổng 3 góc 1 tam giác)

hay góc A+60 độ +40 độ=180độ

  => góc A= 180 độ-60 độ-40 độ.

  => góc A=80 độ

Ta có: góc A>góc B>góc C(vì 80 độ>60 độ>40 độ)

        => BC>AC>AB( Các cạnh và góc đối diện trong tam giác)

HT mik làm giống bạn Dương Mạnh Quyết

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Tiến Phạm
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The Moon
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The Moon
20 tháng 8 2021 lúc 17:54

GẤP LẮM Ạ,NGAY BÂY GIỜ Ạ

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đào khánh lâm
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Nguyễn Lê Phước Thịnh
10 tháng 3 2022 lúc 21:53

Bài 1: 

a: Xét ΔABC có \(AC^2=AB^2+BC^2\)

nên ΔABC vuông tại B

b: XétΔABC có BC<AB<AC

nên \(\widehat{A}< \widehat{C}< \widehat{B}\)

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Kimian Hajan Ruventaren
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