题目
In the sequence above, each term after the first is one-half the previous term. If x is the tenth term of the sequence, then x satisfies which of the following inequalities?
解析
在上述数列中,首项之后的每一项都是前一项的二分之一。如果\(x\)是该数列的第十项,那么\(x\)满足以下哪个不等式?
已知数列\(\frac{1}{2},\frac{1}{4},\frac{1}{8},\frac{1}{16},\frac{1}{32},\cdots\)是首项\(a_{1}=\frac{1}{2}\),公比\(q = \frac{1}{2}\)的等比数列。
根据等比数列的通项公式\(a_{n}=a_{1}\times q^{n - 1}\),可得该数列的第十项\(x=a_{10}=\frac{1}{2}\times(\frac{1}{2})^{10 - 1}=(\frac{1}{2})^{10}=\frac{1}{1024}\)
因为\(\frac{1}{1000}=0.001\)且\(\frac{1}{10000}=0.0001\),而\(\frac{1}{1024}\)介于\(\frac{1}{10000}\)与\(\frac{1}{1000}\)之间,即\(0.0001<\frac{1}{1024}<0.001\)
所以\(0.0001 < x < 0.001\),答案是D选项