问题
填空题
已知等差数列{an}中，a1=2，a10=20，则前20项和S20=______．
答案
∵在等差数列{an}中，a1=2，a10=20
∴公差d=
=2a10 -a1 9
∴s20=20×2+
×20×(20-1)=2301 2
故答案为230
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已知等差数列{an}中，a1=2，a10=20，则前20项和S20=______．
∵在等差数列{an}中，a1=2，a10=20
∴公差d=
=2a10 -a1 9
∴s20=20×2+
×20×(20-1)=2301 2
故答案为230
Americans value competition. They believe that competition out the best in any individual. They claim that it challenges or even each person to produce the very best that is humanly possible. , the foreign visitor will see competition encouraged in the American home and in the American classroom, at the youngest age levels. You may find the placed on competition confusing, especially if you come from a society that promotes cooperation competition among individuals. But Americans teaching in the Third World countries find the lack of competition in a classroom situation equally . They soon learn that what they had thought to be one of the universal human qualities only a particularly American or Western value.
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