Question

已知a,b,a+b成等差数列,a,b,ab成等比数列,且0

1. A.
   m>1
2. B.
   1<m<8
3. C.
   m>8
4. D.
   0<m<1或m>8

Answer 1

C
∵a,b,a+b成等差数列,
∴2b=2a+b,即b="2a.                    
∵a,b,ab成等比数列,
∴b²=a²b,即b=a²(a≠0,b≠0).              
由①②得a=2,b=4.
∵0<log_m8<1,
∴m>1.
∵log_m8<1,即log_m8<log_mm,
∴m>8.
故选C.