>
数学
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已知-7,a
1
,a
2
,-1四个实数成等差数列,-4,b
1
,b
2
,b
3
,-1五个实数成等比数列,则
a
2
−
a
1
b
2
=______.
人气:391 ℃ 时间:2020-06-15 05:17:15
解答
设等差数列的公差为d,等比数列的公比为q,
则有-7+3d=-1,-4•q
4
=-1,
解得d=2,q
2
=
1
2
,
∴
a
2
−
a
1
b
2
=
d
−4
q
2
=
2
−4×
1
2
=-1.
故答案为:-1
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