Окружности ω1 и ω2 пересекаются в точках X и Y, лежат внутри окружности Ω и касаются её в точках A и B. Прямая AB повторно пересекает окружности ω1 и ω2 в точках C и D соответственно. Вписанная в криволинейный треугольник CDX окружность касается стороны CD в точке Z. Докажите, что XZ — биссектриса угла AXB.
Окружности ω1 и ω2 пересекаются в точках X и Y, лежат внутри окружности Ω и касаются её в точках A и B. Прямая AB повторно пересекает окружности ω1 и ω2 в точках C и D соответственно. Вписанная в криволинейный треугольник CDX окружность касается стороны CD в точке Z. Докажите, что XZ — биссектриса угла AXB.
What distinguishes the app from competitors is its use of what's known as channels: Public or private feeds of photos and videos that can be set up by one person or an organization. The channels have become popular with on-the-ground journalists, aid workers and Ukrainian President Volodymyr Zelenskyy, who broadcasts on a Telegram channel. The channels can be followed by an unlimited number of people. Unlike Facebook, Twitter and other popular social networks, there is no advertising on Telegram and the flow of information is not driven by an algorithm. Right now the digital security needs of Russians and Ukrainians are very different, and they lead to very different caveats about how to mitigate the risks associated with using Telegram. For Ukrainians in Ukraine, whose physical safety is at risk because they are in a war zone, digital security is probably not their highest priority. They may value access to news and communication with their loved ones over making sure that all of their communications are encrypted in such a manner that they are indecipherable to Telegram, its employees, or governments with court orders. "The result is on this photo: fiery 'greetings' to the invaders," the Security Service of Ukraine wrote alongside a photo showing several military vehicles among plumes of black smoke. Although some channels have been removed, the curation process is considered opaque and insufficient by analysts. Since its launch in 2013, Telegram has grown from a simple messaging app to a broadcast network. Its user base isn’t as vast as WhatsApp’s, and its broadcast platform is a fraction the size of Twitter, but it’s nonetheless showing its use. While Telegram has been embroiled in controversy for much of its life, it has become a vital source of communication during the invasion of Ukraine. But, if all of this is new to you, let us explain, dear friends, what on Earth a Telegram is meant to be, and why you should, or should not, need to care.
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