Tam giác ABC có góc B<90 độ và góc B= 2 góc C. Trên tia đối của BA lấy E sao cho BE=BH, (H là chân đường vuông góc kẻ từ A xuống BC). EH cắt AC tại D. Chứng minh:
a)DA=DC
b)AE=HC
GIÚP MK VỚI, CHỈ CẦN CÂU B THUI
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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)
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
a: Áp dụng tính chất của dãy tỉ số bằng nhau, ta được:
\(\dfrac{a}{1}=\dfrac{b}{3}=\dfrac{c}{5}=\dfrac{a+b+c}{1+3+5}=\dfrac{180}{9}=20\)
Do đó: a=20; b=60; c=100
Vậy: ΔABC là tam giác tù
`a,` vì Tam giác `ABC` có \(\widehat{A}=110^0\)
`=>` Tam giác `ABC` là tam giác tù.
`b,` Cạnh đối diện của \(\widehat{A}\) là cạnh `BC`
`=>` Cạnh lớn nhất của Tam giác `ABC` là cạnh `BC`
XÉT TAM GIÁC ABC
CÓ: \(\widehat{A}+\widehat{B}+\widehat{C}=180^0\) ( định lí)
THAY SỐ: \(90^0+\widehat{C}=180^0\)
\(\widehat{C}=180^0-90^0\)
\(\widehat{C}=90^0\)
\(\Rightarrow\Delta ABC\) VUÔNG TẠI C ( ĐỊNH LÍ)
CHÚC BN HỌC TỐT!!!!!!!!
3:
góc C=90-50=40 độ
Xét ΔABC vuông tại A có sin C=AB/BC
=>4/BC=sin40
=>\(BC\simeq6,22\left(cm\right)\)
\(AC=\sqrt{BC^2-AB^2}\simeq4,76\left(cm\right)\)
1:
góc C=90-60=30 độ
Xét ΔABC vuông tại A có
sin B=AC/BC
=>3/BC=sin60
=>\(BC=\dfrac{3}{sin60}=2\sqrt{3}\left(cm\right)\)
=>\(AB=\dfrac{2\sqrt{3}}{2}=\sqrt{3}\left(cm\right)\)
b, Trên tia đối của tia HB lấy F sao cho HB = HF. Nối A với F
Xét tam giác AHB và tam giác AHF có
AH: cạnh chung
góc AHB= góc AHF
BH= HF
=> tam giác AHB = tam giác AHF(c-g-c)
=> B1 = góc AFH
=> góc AFH= góc C x2
mà góc AFH = A1 + góc C
=>tam giác AFC cân tại F
=> FA=FC (1)
Vì tam giác AHB = tam giác AHF
=> AB=AF (2)
Từ (1),(2) =>AB = FC
Mà BE = HF (cùng bằng BH)
=>FC+FH = AB+BE
=>AE=HC (đpcm)
Còn câu a làm thế nào bạn?