1,1, 5,7,13,()A.15B.17C.19D.21
1,1, 5,7,13,()
A.15
B.17
C.19
D.21
B.17
C.19
D.21
参考解析
解析:间隔作差。即第三项-第一项,第四项-第二项,所得数列为4、6、8、(10),为公差为2的等差数列,则下一项为10+7=(17)。
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