数列an满足an=-1/3a(n-1)(n≥2),a1=4/3,则a4与a2的等差中项?答案是-20/81啊
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数列an满足an=-1/3a(n-1)(n≥2),a1=4/3,则a4与a2的等差中项?答案是-20/81啊数列an满足an=-1/3a(n-1)(n≥2),a1=4/3,则a4与a2的等差中项?答案
数列an满足an=-1/3a(n-1)(n≥2),a1=4/3,则a4与a2的等差中项?答案是-20/81啊
数列an满足an=-1/3a(n-1)(n≥2),a1=4/3,则a4与a2的等差中项?
答案是-20/81啊
数列an满足an=-1/3a(n-1)(n≥2),a1=4/3,则a4与a2的等差中项?答案是-20/81啊
∵an=-1/3a(n-1)(n≥2)
∴an/a(n-1)=-1/3
∴{an}是等比数列,公比为-1/3
∴a4=a1*q^3=4/3*(-1/3)^3=-4/81
a2=a1q=4/3*(-1/3)=-4/9
∴a4与a2的等差中项为
(-4/81-4/9)/2=-2(1+9)/81=-20/81
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