112+113+114+115+116+117+118+119+120...+190+191得数是几?

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112+113+114+115+116+117+118+119+120...+190+191得数是几?
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112+113+114+115+116+117+118+119+120...+190+191得数是几?
112+113+114+115+116+117+118+119+120...+190+191得数是几?

112+113+114+115+116+117+118+119+120...+190+191得数是几?
有191-112+1=80项
代入等差数列求和公式得
Sn=(a1+an)n/2=(112+191)×80/2=12120
a1是首项,an是末项,m是项数

112+113+114+115+116+117+118+119+120...+190+191=(112+191)*(191-111)/2=303*80/2=12120

一共有191-112+1=80项
(112+191)X80÷2=12120