问题
计算题
计算：1+2+22+23+…+210。
答案
解：设S=1+2+22+23+…+210，
2S =2+22+23+24+…+211，
所以2S-S=211-1，
所以S=211-1。
搜题请搜索小程序“爱下问搜题”
计算：1+2+22+23+…+210。
解：设S=1+2+22+23+…+210，
2S =2+22+23+24+…+211，
所以2S-S=211-1，
所以S=211-1。
| 完形填空。 | ||||
| It was very late when we came out of the cinema. We knew the last train would leave 1 11:15, so we ran as 2 as we could to the station. It was just after 11: 15 when we 3 the station, but the trains often leave a little 4 and there was a train standing at Platform 1(第一站台), so we got in. We 5 for half an hour, then we got 6 . We found the ticket collector and asked him 7 the train was going to leave. "Tomorrow morning at six o clock," he told us. There were 8 taxis outside the station. 9 we walked home. It 10 us nearly two hours. The next morning we felt very tired. | ||||
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