12 целых 7/23- ( 6 целых 18/23-t) =  3 целых 21/23+ 5 целых 19/23

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Andriy: Hi, Olia! Any news from our partner school in Great Britain?
Olia: Hello, Andriy! We got a letter from them yesterday. They have launched the UNESCO World Heritage Project in their school and invite us to participate in it, too.
Andriy: I've heard about UNESCO. The abbreviation stands for the United Nations Educational, Scientific and Cultural Organization. It promotes international co-operation among the countries in the fields of education, science, culture and communication. Am I right?
Olia: Yes, you are right.
Andriy: What sites have they chosen for their project?
Olia: They have decided to write about the sites in Ukraine and we have to choose the sites from the UK.
Andriy: Oh, I see. The project will help us know both countries better.
Olia: This is what the projects exist after all. They help us learn more about the world and people who live in it. 

Прямая АВ пересекает плоскость а под углом 30 градусов. АА1 - перпендикуляр, а ВА1 - проекция АВ на плоскости а. Найдите: 1) ВА1 и АА1, если АВ=24 см; 2) длину проекции ВА1 наклонной АВ, если АА1=8 см; 3) длину наклонной АВ и длину перпендикуляра АА1, если ВА1=15 см.