Cho tam giac ABC có cosA=5/9 , D thuộc cạnh BC sao cho (ABC) ̂=(DAC) ̂, DA=6, BD=16/3. Tính chu vi tam giác ABC.

By Trang Ánh Nam -

Cho tam giac ABC có  , D thuộc cạnh BC sao cho , DA=6, . Tính chu vi tam giác ABC.

 

Giải:

Xét 2 tam giác ABC và ADC ta có:

ü 

ü   chung

ð  ABCDAC

ð 

Ta cũng có:

Mà cos=-cos()

Nên: cos=-cos

=>

=>AB2=AD2+BD2-2AD.BD.cos

 

=>

Thay vào biểu thức đồng dạng ở trên ta có:

Ta có hệ:

 

=>AC2=DC.BC==40,96

=>AC=6,4

Vậy chu vi tam giác ABC là:

AB+AC+BC=9+6,4+9,6=25

Comments

  1. AnonymousAugust 24, 2022 at 4:22 AM

    vẫn đang thắc mắc là 81 vs 36 đâu ra=)))

    ReplyDelete

Post a Comment

Popular posts from this blog

Cho tam giác ABC vuông ở B, kéo dài AC về phía C một đoạn CD=AB=1, góc CBD=30 độ. Tính AC.

By Trang Ánh Nam -
Image
  Cho tam giác ABC vuông ở B, kéo dài AC về phía C một đoạn CD=AB=1, góc CBD=30 o . Tính AC.   Giải: Lấy điểm E trên BD sao cho AB//CE ð ⃤  ABC ~   ⃤  CED ð   ð CE.AD=CD.AB=1.1=1 Gọi x=AC Tac có:  (pitago) Tam giác BCE vuông tại C (vì góc B bằng góc C so le) => Thay vào biểu thức trên(màu đỏ), ta được: =>(x 2 -1)(x+1) 2 =3 ó (x 2 -1)(x 2 +2x+1)=3 ó x 4 +2x 3 +x 2 -x 2 -2x-1=3 ó x 4 +2x 3 -2x-4=0 ó x 3 (x+2)-2(x+2)=0 ó (x+2)(x 3 -2)=0 ó x 3 -2=0  (x+2>0 vì x là số dương) =>
Read more

NBC Washington Correspondent Yamiche Alcindor and former U.S. Attorney Barbara McQuade join Andrea Mitchell to discuss key challenges facing the January 6 Committee ahead of their primetime hearings this week: getting a "distracted nation" to pay attention and understand what's at stake. “I think the biggest challenge for lawmakers here, as they talk about these sort of huge ideas of American democracy and sort of the experiment that we're all living in, benefiting from, possibly being brought to his knees, is whether or not they can make people care,” says Alcindor. “The American public has been groomed to expect high value quick entertainment,” says McQuade. "I think putting together a polished show can be very important."

By -
Image
 NBC News correspondent Yamiche Alcindor worried Democrats would have a difficult time making Americans "care" and pay attention to the January 6 hearings, amid high gas prices, inflation, and a baby formula shortage. Appearing in a MSNBC panel Monday, Alcindor told host Andrea Mitchell that the "biggest challenge" the January 6 House Select Committee faced was getting Americans to have the same level of concern for their investigation. "I think the biggest challenge for lawmakers here as they talk about these sort of huge ideas of American democracy and sort of the experiment that we’re all living and benefiting from possibly being brought to his knees is whether or not they can make people care, Andrea," she said. Link 1 Link 2 Link 3 September 18 Post By Học Để Thi | Breaking News, Latest News and Videos Tranganhnam.xyz ...
Read more

Cuomo, Lemon discuss Trump's comments on race

By Trang Ánh Nam -
Image
Chris Cuomo and Don Lemon discuss President Donald Trump's comments about race after the 2019 Oscars. Be nice if Spike Lee could read his notes, or better yet not have to use notes at all, when doing his racist hit on your President, who has done more for African Americans (Criminal Justice Reform, Lowest Unemployment numbers in History, Tax Cuts,etc.) than almost any other Pres! — Donald J. Trump (@realDonaldTrump) February 25, 2019 The left loves to hate on Trump, calling him a racist and what not. I know Trump can be juvenile sometimes – certainly – but the racist and hateful name-calling is just what it is, garbage.
Read more