Many people love going on a trip by plane, because planes are fast. But an airport(机场) is usually far away from the city, and it usually takes hours to get out of the airport and into the city. You have to get there and wait for the plane to take off for hours. You can not open the window, and you can not have delicious food. I like travelling by train. I think trains are the safest(最安全的). Train stations are usually in cities. When you are late for a train, you can catch another one. You can walk around in the train and look out of the window. You can see many interesting things on your way. I know it takes some time. I also like cars. You can start your trip when you want to, and you don’t need to get to a station. You can carry many things with you, too. But sometimes there are many cars on the road. 小题1:Many people like travelling by plane because_____________.
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A为n阶矩阵, 证:tr(A^k)=A的各个特征值的k次方之和
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你能帮帮他们吗