Question

等比数列中,a3*a4*a5=3 ,a6*a7*a8=24则a9*a10*a11的值等于多少

Answer 1

设a1=m,a2=km,a3=k^2m,a4=k^3m…an=k^(n-1)m

a3*a4*a5=k^2*k^3*k^4m^3=k^9m^3=3

a6*a7*a8=k^5*k^6*k^7m^3=k^18m^3=24

得:k^9=8;m^3=3/8

则a9*a10*a11=k^8*k^9*k^10m^3=k^27m^3

=(k^9)^3m^3

=8^3*3/8

=3*64

=192