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  3. The numbers 3, 10, 17, 24, 31, and 38 are the first six terms of an infinite seq

The numbers 3, 10, 17, 24, 31, and 38 are the first six terms of an infinite seq

游客2025-02-24  30
问题 The numbers 3, 10, 17, 24, 31, and 38 are the first six terms of an infinite sequence in which each term after the first is 7 greater than the preceding term. What is the 45th term of the sequence?
选项 A、308
B、311
C、312
D、315
E、318
答案 B
解析 数字3，10，17，24，31和38是一个无穷数列(infinite sequence)的前六项，该数列的每一项都比前一项大7，问这个数列的第45项是多少?
解：本题的正确答案是(B)。由题意可知，该数列是一个等差数列，其首项a1=3，其公差为d=7，根据等差数列的通项公式可得：a45=a1+(n-1)d=3+(45-1)×7=311
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