问题 填空题
各项均为正数的等比数列{an}满足a1a7=4,a6=8,函数f(x)=a1x+a2x2+a3x3+…+a10x10,则f(
1
2
)=______.
答案

∵正数的等比数列{an}满足a1a7=4,∴

a24
=4,可得a4=2,

∵a6=8,

a6
a4
=q2,可得q2=4,可得q=2,∴a1×q3=2,得a1=
1
4

∴an=a1×qn=

1
4
×2n-1=2n-3

∴f(x)=a1x+a2x2+a3x3+…+a10x10

∴f(

1
2
)=a1
1
2
+a2
1
2
2
+a3
1
2
3+…+a10
1
2
10=
1
23
+
1
23
+…+
1
23
=10×
1
23
=
10
8
=
5
4

故答案为

5
4

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