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smc

algebra senior

Problem

Given the sequence , the smallest value of n such that the product of the first members of this sequence exceeds is:
(A)
(B)
(C)
(D)
(E)
Solution
Note that the given sequence is a geometric sequence with a common ratio . Let the product of the first terms of the sequence be denoted . It is a consequence of the laws of exponents that , , and, in general, , where denotes the th triangular number. Setting equal to , we see that: Because must be positive, we are left with . Given this information, choice (D) may seem appealing. Do not be fooled. The product of the first terms is exactly , but the problem asks for the smallest such that exceeds 100,000. Thus, the minimum value of which satsifies the problem is .
Final answer
E