问题
选择题
已知-9,a1,a2,-1四个实数成等差数列,-9,b,-1三个实数成等比数列,则b(a2-a1)=( )
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答案
∵-9,a1,a2,-1四个实数成等差数列,∴-1=-9+3(a2-a1),解得a2-a1=
.8 3
∵-9,b,-1三个实数成等比数列,∴b2=-9×(-1),解得b=±3.
∴b(a2-a1)=±3×
=±8.8 3
故选C.
已知-9,a1,a2,-1四个实数成等差数列,-9,b,-1三个实数成等比数列,则b(a2-a1)=( )
|
∵-9,a1,a2,-1四个实数成等差数列,∴-1=-9+3(a2-a1),解得a2-a1=
.8 3
∵-9,b,-1三个实数成等比数列,∴b2=-9×(-1),解得b=±3.
∴b(a2-a1)=±3×
=±8.8 3
故选C.