Hình Học 9 - Tuấn Anh



Cho tam giác ABC có 3 góc nhọn vs AB<AC nội tiếp (O;R) vẽ 3 đường cao AD , BE, CF cắ nhau tại H cua tam giác ABC

a) CM tứ giác BFEC nội tiếp,xác định tâm của đường ngoại tiếptứ giác BFEC
b) Đường thẳng EF lần luọt cắt AD tại I và CB tại K. cm DA là phân giác cua góc FDE từ đósuy ra KE.FI=IE.FK
c) Gọi T là điểm dối xứng của A qua E ,KT cắt AD tại P.CM PF song song Ac
d) Tính số đo góc A nếu biết tứ giác BOTC nội tiếp 1 đường tròn
giải:
a.     chứng minh tứ giác BFEC nội tiếp – Tìm Tâm.
Ta có:
ü tam giác BFC vuông tại F (gt)
=>tam giác BFC nội tiếp đường tròn có đường kính BC
ü Tam giác BEC vuông tại E (gt)
=>tam giác BEC nội tiếp đường tròn đường kính BC
Vậy 2 tam giác BEC và BFC cùng nội tiếp đường tròn đường kính BC
=>tứ giác BEFC nội tiếp đường tròn đường kính BC
Suy ra tâm I của đường tròn đó là trung điểm của BC.
(ở đây thầy quên để ý câu b có điểm I nên lở lấy rồi, vẽ hình lại khổ lắm, mấy đứa đổi lại điểm khác nhé.)
b.     Chứng minh DA là phân giác của góc FDE => KE.FI=IE.FK
ở đây thầy dùng 2 đường tròn màu hồng vào màu đỏ để chứng minh.
ü Tứ giác CDHE nội tiếp (vì có 2 gốc vuông đối nhau)
=> (góc nội tiếp cùng chắn cung HE)  (1)
ü Tứ giác ACDF nội tiếp (vì có 2 góc vuông cùng nhìn cạnh AC)
=> (góc nội tiếp cùng chắn cung  DA)
=> (cái này chỉ đổi tên 2 tằng trên lại cho đẹp) (2)
Từ (1) và (2) suy ra: 
Vậy AD là phân giác của tam giác FDE.
Áp dụng tính chất phân giác của tam giác FDE ta có:
lại có: KDAD (gt)
suy ra: KD là phân giác ngoài của tam giác FDE, ta có:
từ (*) và (**) suy ra:
=>EI.KF=EK.FI (điều phải chứng minh)
Thầy giải rồi mà quên mất, làm cho mình phải thức khuya, buồn. Tuấn Anh bài này giải rồi mà lại quên nha, bỏ game lo học đi.


Read More Add your Comment 1 comments


20 Things Other Than Napster Released in 1999




20 Things Other Than Napster Released in 1999

Napster was born on June 1, 1999, in Shawn Fanning's Northeastern University dorm room, and music was forever revolutionized.
The service pioneered peer-to-peer file sharing, meaning it allowed users to transfer files directly between each other. Prior to Napster, downloading music off the internet was unreliable.

But two years later, the Record Industry Association of America filed lawsuits against Napster users who illegally downloaded music and the service was shut down. Napster may be gone, but its legacy will live on.
Music wasn't the only thing set free 15 years ago. Take a trip with us down memory lane and relive the final year of an innovative century.


Read More Add your Comment 0 comments


House approves 'media shield' amendment, as reporter reveals 2011 subpoena fight



houseofrep232way_wide-4bac6d92f39d630d0f94f3c708ca06710a717d2f-s6-c30

The House of Representatives today voted 225-183 to approve an appropriations bill amendment that bars the Justice Department from forcing reporters to testify about their confidential sources.
"Advocates for journalists have tried for years to enact a federal 'media shield' bill allowing judges to quash such subpoenas," reports Charlie Savage at the New York Times. "The legislation, sponsored by Representative Allan Grayson, Democrat of Florida, has a long way to go before it would become law."
h
In related news, a former Fox News reporter this week shared more about his 2011 subpoena fight. In a report on the ABC News website, where he now works, Mike Levine explains that he was subpoenaed in January 2011 about his sources for a 2009 story. Levine fought the order, and the Justice Department dropped it in April 2012.
At abcnews.com, Levine writes:
It’s unclear what that will mean for the Times’ Risen, who is now asking the U.S. Supreme Court to weigh in on his case after a federal appeals court ruled against him. But in what might be the only other instance of Holder’s Justice Department subpoenaing a reporter to testify about his confidential sources, federal prosecutors ultimately backed down.
“The reporter” in this second, previously undisclosed case is the author of this article. In January 2011, while I was working for Fox News, the Justice Department persuaded a federal grand jury in Washington to subpoena me for my confidential sources after I reported two years earlier that several Somali-Americans were secretly indicted in Minneapolis for joining an al Qaeda-linked group in Somalia.
Professional and personal life under the threat of jail for 16 subsequent months is best captured in a note I wrote to myself at the time: “I've felt like throwing up all day so far … Just that 'racing heart' feeling throughout."
Still, I felt I had to protect my confidential sources.
U.S. Attorney General Eric Holder addresses reporters at a news conference at the Justice Department in Washington, D.C. on May 14, 2013. Jonathan Ernst/Reuters

U.S. Attorney General Eric Holder addresses reporters at a news conference at the Justice Department in Washington, D.C. on May 14, 2013. Jonathan Ernst/Reuters
And again, from Charlie Savage's report at the Times:
The subpoena is the second of its kind to come to light under the Obama administration, which also has tried to force James Risen, a reporter for The New York Times, to testify in the trial of a former Central Intelligence Agency officer charged with leaking to him. A federal appeals court has ruled that Mr. Risen must testify. He has appealed that ruling, and the Supreme Court may announce as soon as Monday whether it will hear the case.
[Thanks, Josh Stearns]


Read More Add your Comment 0 comments


Violent birth of a star, as seen from NASA Hubble Space Telescope



potw1421a

An image released from NASA's Hubble Space Telescope shows IRAS 14568-6304, a young star shrouded in golden gas and dust.
It appears to be embedded within an intriguing swoosh of dark sky, which curves through the image and obscures the sky behind.
This dark region is known as the Circinus molecular cloud. This cloud has a mass around 250 000 times that of the sun, and it is filled with gas, dust and young stars. Within this cloud lie two prominent and enormous regions known colloquially to astronomers as Circinus-West and Circinus-East. Each of these clumps has a mass of around 5000 times that of the sun, making them the most prominent star-forming sites in the Circinus cloud.
The clumps are associated with a number of young stellar objects, and IRAS 14568-6304, featured here under a blurry fog of gas within Circinus-West, is one of them.
IRAS 14568-6304 is special because it is driving a protostellar jet, which appears here as the "tail" below the star. This jet is the leftover gas and dust that the star took from its parent cloud in order to form. While most of this material forms the star and its accretion disc — the disc of material surrounding the star, which may one day form planets — at some point in the formation process the star began to eject some of the material at supersonic speeds through space. This phenomenon is not only beautiful, but can also provide us with valuable clues about the process of star formation.
More about the infant star at NASA's website.


Read More Add your Comment 0 comments


The dream of libertarian technotopia floating startup nations



Image: Bloomberg
From Bloomberg's Edward Robinson, a feature on the nonprofit Seasteading Institute.

"The five-year-old organization is pursuing an ambitious aquatic mission: to develop floating microcountries that will dwell in international waters with the same sovereign status enjoyed by cruise ships. Think secessionist, do-it-yourself nation building meets the 1995 post-apocalyptic science-fiction stinker ‘Waterworld.’"
They're based in Oakland, CA, and operating on $1.2 million in seed cash from PayPal billionaire Peter Thiel.


Read More Add your Comment 0 comments


Apple's Smart Home Initiative Is Probably Just a Certification Program



Wwdc

As you were, Apple smart home hopefuls.
Contrary to rumors published in the Financial Times that emerged earlier this week that Apple will be rolling out its own home automation technology, it seems that the Cupertino company will instead be ensuring that existing products conform to a standard, similar to what Made for iPhone does for accessories, according to a report from GigaOm.
Initially, it was thought that Apple would offer an iOS-powered smart home system, creating a platform for developers to build on. That way, those developers could more easily offer products that do things such as automatically turning on house lights at the detection of the homeowner's iPhone. However, it now appears that Apple is working toward certifying smart home devices that with iOS support, such as the Nest thermostat, which Google acquired in January.
Apple was expected to debut its new smart home system at its annual Worldwide Developers Conference beginning June 2 in San Francisco. WWDC will supposedly see the launch of Healthbook, an app dedicated to tracking health-related data, including blood pressure rates, exercise time and hours of sleep per night. In addition, the conference will also most likely preview iOS 8 and the newest OSX.
Apple representatives did not immediately respond to a request for comment.


Read More Add your Comment 0 comments


Apple iWatch Parody Will Make You Question Every Wearable Gadget



Another week, another unnecessary tech product.
The newest craze in gadgets-we-don't-really-need? Wearable devices, namely Apple's hotly anticipated iWatch.

Mathius, a Youtube channel known for poking fun at technology, chose the mysterious iWatch as the target for its latest parody. And despite how excited some may be for the new product, this video proves how totally unnecessary it is.
Apple, watches are already doing a fine job telling time — and if it ain't broke, don't fix it.
Have something to add to this story? Share it in the comments.


Read More Add your Comment 0 comments


Trading Barbs With the NSA? Just Another Day for Edward Snowden



Edward-snowden1
NSA whistleblower Edward Snowden during a meeting with German Green Party MP Hans-Christian Stroebele regarding being a witness for a possible investigation into NSA spying in Germany, on Oct. 31, 2013 in Moscow, Russia.

NSA whistleblower Edward Snowden, who has provided a trove of evidence to show how the agency spies on Americans as well as other governments, was again assailing the NSA on Friday for doing something he considered untruthful.
On Thursday, the agency released a single email Snowden sent while he worked as a contractor at the NSA. In it, Snowden asked a legal question about whether executive orders have precedence over federal statute law. His question apparently referenced a portion of text from an NSA training manual he felt was incorrect.
Snowden has always said he tried to relay his concerns to the agency before going public with them, but the NSA has denied this claim. When Snowden restated this position during a Wednesday interview with NBC, the NSA released the single email mentioned above.
Which brings us to Friday's happenings.

Snowden: NSA's email release is incomplete

In an interview with the Washington Post, Snowden called the NSA's release "incomplete" and said the agency released the single document to gain a "political advantage."
Snowden also brought up the fact that the NSA had previously said he had made no attempts to contact them with concerns, which this email proves to be untrue.
Snowden then mentioned that Senators Ron Wyden (D-Oregon) and Mark Udall (D-Colorado) knew about the NSA's mass surveillance in 2011 and thought it was "abusive," but felt they could do little about it. That alone, he said, "underscores how futile such internal action is—and will remain—until these processes are reformed."

Senator Udall's office responds to Snowden

Senator Udall's office offered a tepid response to Snowden's claim that Udall and Wyden have been unable to enact meaningful reform from inside the system.
Udall "did not feel constrained" by being a part of the government, Mike Saccone, a spokesperson for Senator Udall, told Mashable. Saccone said Udall has worked since 2011 to "rein in" the NSA's mass data collection, but fixing organizational missteps through the Senate takes time.
The spokesperson also said that Udall still believes Snowden should return to the U.S. to make his case.

Former government whistleblower says Snowden wouldn't get a fair trial

Daniel Ellsberg, whose leaking of the Pentagon Papers in 1971 made him the Edward Snowden of the the Vietnam War, wrote in The Guardian on Friday that Snowden would not receive a fair trial if he came home.
Ellsberg was responding to Secretary of State John Kerry's call for Snowden to "face the music" on Wednesday, saying that no whistleblower can expect a fair trial until the Espionage Act is reformed. The former intelligence leaker said that the act—originally meant to prevent military insubordination during a time of war—was now being used to prevent whistleblowers from defending themselves in court.
That's what happened to him, Ellsberg wrote, so why wouldn't it happen to Snowden?


Read More Add your Comment 0 comments


An Ode to Jay Carney




White House Press Secretary Jay Carney resigned on Friday, which is the perfect opportunity to dig up some of his greatest hits, ranging from the moment he nervously stepped into the press briefing room in 2011 to the more recent endearing exchange about this new beard.

Carney has held his post as press secretary since Feb. 11, 2011, and bearing the brunt of endless media requests is no easy feat. So take a moment to embrace all his awkward exchanges and humor enveloping the press briefing room in the video above.

Obama gives Jay Carney a hug after announcing he will step down later next month on May 30, 2014.
IMAGE: SUSAN WALSH/ASSOCIATED PRESS
Have something to add to this story? Share it in the comments.


Read More Add your Comment 0 comments


Mario Kart 8 Content Pack Adds Mercedes-Benz SUV



Mario-kart-mercedese

In what has got to be one of the strangest franchise crossovers we’ve ever seen, a forthcoming DLC (downloadable content) pack for Mario Kart 8 will allow gamers to hop behind the wheel of a Mercedes-Benz.
Mario Kart screen shot

IMAGE: THE OFFICIAL NINTENDO MAGAZINE
Nintendo’s Mario Kart 8 is released in Japan Friday—as is the new Mercedes-Benz GLA SUV convertible. To celebrate this fortuitous coincidence the two companies have teamed up to produce the in-game “GLA Kart," which will be available to download in Japan this summer.

This isn’t the first time Nintendo has utilised product placement in their games:Eurogamer.net reports that Pikmen 2 contained multiple discoverable licensed items, including Duracell batteries, whilst “Wave Race 64 featured Kawasaki jet skis.”
Mario and Mercedes car

IMAGE: THE OFFICIAL NINTENDO MAGAZINE
In a statement on whether the DLC would be available elsewhere, Nintendo UK said that "the announcement this time was made by Mercedes-Benz Japan regarding their collaboration in Japan with NCL."
"As for the information relating to the distribution of the GLA kart for MK8 outside Japan, we will be able to announce in the near future."
Sounds promising, then.
Another new tie-in between Mercedes-Benz Japan and Nintendo comes in the form of what at first appears to be a playable version of the Mercedes-driving Mario seen in the advert embedded above. But when you click through to play, it's actually one big advert that you click on to finish the level. Sneaky.
Before you start gnashing your teeth about advertising and exorbitantly-priced add-ons: Remember, the DLC is free!


Read More Add your Comment 0 comments


Did Anyone Order a Slice of Pizza Poetry?



At the touch of love, everyone becomes a poet — and there is no greater love than pizza.
Professional pizza man Steve Richardson who owns the Tumblr blog Every Pizza I've Ever Delivered, featuring stories of delivery men and the delicious carbs they carry.

Let these funny, strange and sometimes heartbreaking tales waft over you like the fragrance of a fresh pie. Life as a peddler of cheesy, doughy goodness may not be glamorous, but these guys have enough soul to make Shakespeare weep into his slice of pepperoni.


Read More Add your Comment 0 comments


 

© 2012 Học Để ThiBlog tài liệu