等差数列{an}的前n项和记为Sn,已知a10=30,a20=50。 (Ⅰ)求通 发布时间:2017-04-30 10:33 │ 来源:www.tikuol.com 题型:解答题 问题: 等差数列{an}的前n项和记为Sn,已知a10=30,a20=50。(Ⅰ)求通项an;(Ⅱ)若Sn=242,求n。
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题型:解答题 3A的直流电通过电阻R时,t时间内产生的热量为Q;现让一交流电通过电阻R,若2t时间内产生的热量为Q,则该交流电流的有效值和最大值分别为( )A.I有=3/2A,Im=3AB.I有=3A,I有=3AC.I有= A,I有 AD.I有3A,Im=6A 查看答案