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2 天前 · The Global Positioning System ( GPS ), originally Navstar GPS, [2] is a satellite-based radio navigation system owned by the United States government and operated by the United States Space Force. [3] .
1 天前 · The 828-metre (2,717 ft) tall Burj Khalifa in Dubai has been the tallest building since 2010. The Burj Khalifa has been classified as megatall. A diagram showing the tallest buildings as of 2024 This is a list of the tallest buildings.Tall buildings, such as skyscrapers, are intended here as enclosed structures with continuously occupiable floors and a height of at least 340 metres (1,120 ft).
5 天前 · Viète. de Moivre. Euler. Fourier. v. t. e. In trigonometry, trigonometric identities are equalities that involve trigonometric functions and are true for every value of the occurring variables for which both sides of the equality are defined. Geometrically, these are identities involving certain functions of one or more angles.
2 天前 · The geologic time scale or geological time scale ( GTS) is a representation of time based on the rock record of Earth. It is a system of chronological dating that uses chronostratigraphy (the process of relating strata to time) and geochronology (a scientific branch of geology that aims to determine the age of rocks).
2 天前 · The number π (/paɪ/; spelled out as "pi") is a mathematical constant that is the ratio of a circle's circumference to its diameter, approximately equal to 3.14159. The number π appears in many formulae across mathematics and physics. It is an irrational number, meaning that it cannot be expressed exactly as a ratio of two integers, although ...
13 小時前 · Major events. Flight paths of the four planes used on September 11. 7:59 a.m.: American Airlines Flight 11, a Boeing 767 with registration number N334AA, carrying 76 passengers (excluding the hijackers) and 11 crew members, departs 14 minutes late from Logan International Airport in Boston, bound for Los Angeles International Airport.
2 天前 · Chicago is the most populous city in the U.S. state of Illinois and in the Midwestern United States.With a population of 2,746,388, as of the 2020 census, it is the third-most populous city in the United States after New York City and Los Angeles.As the seat of Cook County, the second-most populous county in the U.S., Chicago is the center of the Chicago metropolitan area, often colloquially ...
