1-22+32-42+52-62+...+992-1002=?简便方法
1-22+32-42+52-62+...+992-1002=?简便方法
数学人气:162 ℃时间:2020-03-29 22:10:05
优质解答
1-22+32-42+52-62+...+992-1002=1-(22-32)-(42-52)-(62-72)-...-(982-992)-1002 =1-(-10)×49-1002=1+490-1002=-511解析:中间项共有1+(98-2)/2=49个,所以第二步中1-(-10)×49-1002.
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