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ngohamy9x
2 năm trước
Cho tam giác abc,đường phân giác bd và ce. Biết ad/dc=2/3, ae/eb=5/6.tính các cạnh của tam giác abc, chu vi tam giác là 45cm
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In the early 1900's, the world was developing at a very rapid pace, and with the growth of industrialization, cities became more crowded. Furthermore, with the invention automobiles, the traffic on the roads increased significantly, so there was a need for a better traffic system. In 1912, an American policeman, Lester Wire, who was concerned with the increasing traffic, came up with the idea of the first electric traffic light. Based on Wire's design, the lights were first installed in Cleveland, Ohio, on August 5, 1914, at the corner of 105th and Euclid Avenue. The first electric traffic light had only red and green lights; it did not have a yellow light like modern- day traffic signals. Instead of a yellow light, it had a buzzer sound that was used to indicate that the signal would be changing soon. In the year 1920, a policeman named William Potts in Detroit, Michigan invented the first four-way and three-coloured traffic lights. Apart from red and green, a third colour - amber (or yellow) - was introduced. Detroit became the first city to implement the four-way and three-colored traffic lights. In the 1920's, several automated traffic signals were installed in major cities around the world. The modern traffic light still uses this famous T-shaped model with three different colors. 31. Due to the invention of cars, the traffic on the roads increased rapidly. T/ F 32. The first electric traffic light was invented in 1914 by Lester Wire. T/ F 33. The first electric traffic light had red, green and amber lights. T/ F 34. The yellow light didn’t exist until the 1920s. T/ F 35. Detroit was the first city to use the red, yellow, and green lights to T/ F control road traffic.

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