等比数列:(3)a5=4,a7=6,求a9 (4)a5-a1=15,a4-a2=6等比数列:(3)a5=4,a7=6,求a9 (4)a5-a1=15,a4-a2=6,求a3.过程写在纸上拍照发来,

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等比数列:(3)a5=4,a7=6,求a9 (4)a5-a1=15,a4-a2=6等比数列:(3)a5=4,a7=6,求a9 (4)a5-a1=15,a4-a2=6,求a3.过程写在纸上拍照发来,
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等比数列:(3)a5=4,a7=6,求a9 (4)a5-a1=15,a4-a2=6等比数列:(3)a5=4,a7=6,求a9 (4)a5-a1=15,a4-a2=6,求a3.过程写在纸上拍照发来,
等比数列:(3)a5=4,a7=6,求a9 (4)a5-a1=15,a4-a2=6
等比数列:(3)a5=4,a7=6,求a9 (4)a5-a1=15,a4-a2=6,求a3.过程写在纸上拍照发来,

等比数列:(3)a5=4,a7=6,求a9 (4)a5-a1=15,a4-a2=6等比数列:(3)a5=4,a7=6,求a9 (4)a5-a1=15,a4-a2=6,求a3.过程写在纸上拍照发来,
a7^2=a5a9
a9=a7q^2
∴a9与a7同号
a9=9
4)求什么?

8
4

公比为q
a7=a5*q^2
解得q^2=3/2
a9=a7*q^2=6*(3/2)=9

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