В геометрической прогрессии b1+b2=30 b2+b3=20. Найдите первые три члена прогрессии - Дата: 24.12.2019, Автор: clancy - №6468113

В геометрической прогрессии b1+b2=30 b2+b3=20. Найдите первые три члена прогрессии
- Предмет:
  Алгебра
- Автор:
  clancy
- 6 лет назад

Ответы 1

b1+b1q=30 b1(1+q)=30 b1×20/b1q=30 20q=30 b1q+b1q^2=20 b1q(1+q)=20 1+q=20/b1q q=20/30 q=2/3dalwe naidew cama)))))
- Автор:
  grant
- 6 лет назад
- 0
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перевод текста
For the first time the idea of building the underground railway in Moscowwas discussed before the revolution. However, the construction of the firstsection (from Sokolniki to Central Park) was initiated only in 1932. It lasted3 years and was called the record period by the world press. The Russianengineers carefully studied the existing underground systems abroad before working out their own project, which represented a significant improvement ofthe London system.The engineering difficulties were great mainly because much of the soilwas composed of running sand*. Fortunately most of the running sand layclose to the surface and it was found possible to use out-and-cover method**of construction under many of the streets. However, in the city center wherethe line is 100 ft or deeper, the construction of tunnels was necessary.The Moscow Underground consists of a circle line, which runs round thecity center, several radial lines crossing the city and connecting with eachother and the lines running to the countryside. Some constructional work isstill going on. Now the length of the underground lines has reaches about300 km.At present, the Moscow Metro handles more than five million passengerseach day. During peak hours trains run at a speed of 90 km/h with theintervals of about 80 seconds. One train takes up to 1,500 passengers.For greater safety of travel, all trains are inspected every 6-9 hours ofrunning. Being in operation for about 13 hours daily each Metro train coversthe distance equal to that from Moscow to St. Petersburg. The trains servicingthe Underground are supplied with low voltage direct current. The current isobtained from the third rail by special devices that are mounted beneath themotor coaches. Rolling stock is completely replaced approximately onceevery four years.The Moscow Metro can compete with the underground railways in any ofthe European capitals in level of automation. At present, the experiments arebeing conducted with an “automatic driver”, i.e. with computer-controlledtrains. The computer devices will help to relieve the nervous strain on thedrivers and make it possible to increase the cruising speed*** of trains evenmore. These automatic devices have already been tested over the CircleRoute by way of experiment.
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