The Republic of Belarus is situated in the centre of Europe. It borders on Latvia, Lithuania, Belarus, the Ukrain, Russia and Poland. La. territory ifs much larger then such countries as Austria, Belgium, Bulgaria, Greece and the number of others. Its present population is about 12 million people. Belarus is a land of vast plains and picturesque hills, thick forests and green meadows, deep blue lakes and flowing rivers. Forests cover 2/5 of Belarus, they are scattered all over the country. There are a lot of rivers and lakes are in our country. The Dnieper, Pripyat, Beresins, Sozh, Zapadnaya Dvina, Neman are the biggest rivers with more then 500 kilometers in length. The largest lake in Belarus is lake Naroch which stretches 13 kilometers from West to East. It is very popular recreation aria in our country. Belarus has a moderately continental climate due to Atlantic influences with a worm winter and with a worm summer. TO most of the world Belarus is relatively known, a new country in the central Europe. To its people it's an ancient land. The history of Belarus goes back to ancient times beginning with the Polotsk Principality in the 10th century. From the 13th centuiy till the 16th centuiy the territory of present -day Belarus was the core of the Grand Duchy of Lithuania in which Belarussian was the official language. It was one of the largest, most powerful and flourishing state*, in Eastern Europe. The 16th century is considered to be the Golden Age of Belarussion history. In this period there was a wide growth of old and the foundation of many new cities and towns. There occurred significant processes in culture and economy of Belarussian people. As Belarus is situated in the centre of Europe many wars took place in its territory. One of the greatest wars was in 1812 when the emperor Napoleon attacked Russia. And Belarussian lands became the arena, of military actions. A great number of Belarussians took part in this war against Napoleon. hi the 20th century alone Belarus has lived through three revolutions and three bloody wars. The Great Patriotic War of 1941-1945 is one of the most heroic and tragic periods in the history of the centuiy. For three years the territory of Belarus was occupied by the Nazi. The country lost more then 3 million people (every third citizen felt in the fight against fascism), many towns and villages were ruined. Belarus lost more then half of its national wealth-Today Belarus is a developed industrial state. Industry makes up 70% of the Gross National Product. The main industries are engineering, chemical industry, wood-working industry, light and food industries. The major industrial centres in Belarus are Minsk, Gomel, Vitebsk, Mogilev, Soligorsk, Zhodino, Brest and others. Belarussian goods are exported to many countries and known, all over the world. Agriculture of Belarus specializes in milk and meet production, flax, vegetables (especially potatoes) and-fruit (especially apples). The Republic of Belarus has well-developed science and educational system- The Academy of Sciences found in 1929 is one of the largest centres of science in our country. Its research-institutes work on various important problems in such fields as mathematics, optics, genetics, biology, etc. The demand for higher education remains high. State institutions are the centres both for education and scientific research. Nowadays in Belarus there are 43 universities, academies and institutes which provide training in various spheres of science and humanities. Ai present Belarus actively participates in an effective international partnership with the government of different states and international organizations. As so-founder of the United Nati6nals Belarus contacts with various institutions and organizations of the United Nationals, World Bank, World Health Organization, International Labor Organization, UNESCO, the European Union, etc. Belarus cooperates with such countries as Germany, Denmark, France, Canada, Italy, Netherlands, Sweden, Great Britain, The USA and many others.
В одной из них должны находится точка F, поскольку длина отрезка FA = 11.
Выбрав левую или правую ориентацию точки F мы придём к одной или другой конструкции точек, которые будут отличаться друг от друга – как отражение в зеркале (flip), поэтому в любом случае, крайние точки конструкции и там и там будут одни и те же (у ботинка есть пятка и носок – это его крайние точки, у отражённого в зеркале ботинка тоже есть пятка и носок – те же крайние точки, хоть и обращённые).
Итак, нам безразлично, с какой стороны выбирать положение точки F, поэтому для минимизации усложнений в рассуждениях выберем точку F с положительной координатой F (11) .
Аналогично, точка B может быть расположена на числе 1 или –1, поскольку оба этих числа удалены на единицу от нуля. Теперь, когда положение точки F(11) уже выбрано – выбор точки B на числе (-1) приведёт к тому, что точка B(–1) будет расположена за пределами отрезка AF, а выбор точки B на числе (1) приведёт к тому, что точка B(1) будет расположена внутри отрезка AF. Поэтому выбор числа для точки B – вопрос важный и принципиальный, который уже нельзя решать случайным произвольным выбором. Итак, пусть B – это какое-то число, либо (1), либо (–1), какое именно, мы пока не знаем, но выясним это в процессе решения.
Так что мы можем записать, что
Теперь точка C. Она удалена от точки B на 3, поскольку отрезок BC=3. Куда именно нужно отступать от точки B – влево или вправо, мы опять же не знаем.
Так что мы можем записать, что
Аналогично, точка D. Она удалена от точки C на 4, поскольку отрезок CD=4.
Так что:
Точка E удалена от точки D на 5, поскольку отрезок DE=5.
Точка F удалена от точки E на 10, т.к. отрезок EF=10.
Но ведь мы знаем, что F=11, тогда:
даже если сложить все слагаемые слева, то 21 никак не наберётся, значит:
никакие комбинации знаков слева не могут обнулить выражение, а значит:
никакие комбинации знаков слева не сравняют выражение с пятёркой, а значит:
отсюда ясно, какие нужно использовать знаки:
восстанавливаем выражение в обратную сторону:
Т.е.: B = –1 ; C = –1+3 = 2 ; D = –1+3 + 4 = 2+4 = 6 ; E = –1+3+4 – 5 = 6 – 5 = 1 ; F = –1+3+4–5 + 10 = 1 + 10 = 11 ;
