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对于两个相似三角形,如果沿周界按对应点顺序环绕的方向相同,那么称这两个三角形互为顺相似;如果沿周界按对应点顺序环绕的方向相反,那么称这两个三角形互为逆相似.例如,如图①,△ABC∽△A′B′C′,且沿周界ABCA与A′B′C′A′环绕的方向相同,因此△ACB和△A′B′C′互为顺相似;如图②,△ABC∽△A′B′C′,且沿周界ABCA与A′B′C′A′环绕的方向相反,因此△ACB和△A′B′C′互为逆相似.

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    The first ancient Olympic Games for which we still have written records were held in 776 BC. Coroebus won the only event at the Olympics. This made him the very first Olympic champion in history. Then they grew and continued to be played every four years. In 393 AD, the Roman emperor Theodosius Ⅰ, a Christian, announced to end the Games because of their pagan (异教的) influences.

    About 1,500 years later, a young Frenchman named Pierre de Coubertin began their revival (恢复). In 1892 Coubertin first brought forward his idea to revive the Olympic Games but failed.

    Two years later, Coubertin organized a meeting with 79 delegates (代表) who represented nine countries. At this meeting he got what he wanted. All the delegates at the conference voted for the Olympic Games. They also decided to have Coubertin set up an international committee to organize the Games. This committee became the International Olympic Committee (IOC) and Demetrious Vikelas from Greece was selected to be its first president. Athens was chosen for the revival of the Olympic Games and the planning was begun.

    The very first modern Olympic Games opened in the first week of April, 1896. Since the Greek government had been unable to afford a stadium, a rich Greek architect, Georgios Averoff, donated one million drachmas (over $100,000) to repair the Panathenaic Stadium, originally built in 330 BC.

    Since the Games were not well publicized internationally, contestants (选手) were not nationally chosen but rather came individually and at their own expense. Some contestants were tourists who happened to be in the area during the Games.