问题
填空题
等比数列{an}中，若a3和a13是方程2x2-21x+8=0的两个根，则a8=______．
答案
由题意可得，a3•a13=4
由等比 数列的性质可得，a3•a13=a82=4
∴a8=±2
故答案为：±2
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等比数列{an}中，若a3和a13是方程2x2-21x+8=0的两个根，则a8=______．
由题意可得，a3•a13=4
由等比 数列的性质可得，a3•a13=a82=4
∴a8=±2
故答案为：±2
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