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已知等比数列{an}中,a5=4,a7=6,求a9
人气:406 ℃ 时间:2020-04-05 04:30:15
解答
方法1:
a7 = a5 * q^2 (设q是公比)
则q^2 = a7/a5 = 3/2
a9 = a7× q^2 = 6 * 3/2 = 9
方法2:
a7*a7=a5*a9
所以,a9=9
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