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求助OG PS157题
For any positive integer n, the sum of the first n positive integers equals n(n+1)/2 . What is the sum of all the even integers between 99 and 301 ?
为什么答案2﹝150（150+1）/2﹞-2﹝49(49+1)∕2﹞中 两个括号前要乘以2…… 谢谢 |
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