{an}等比数列,且an>0,a1*a100=100 则 lga1+lga2+...+lga100=
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{an}等比数列,且an>0,a1*a100=100 则 lga1+lga2+...+lga100=
lga1+lga2+...+lga100=lga1*a2*.*a99*a100
由{an}等比数列,得
a1*a100=a2*a99=a3*a98=.=a50*a51=100
而a1*a2*.*a99*a100=a1*a100*a2*a99*a3*a98*.*a50*a51=100^(100/2)=100^50=10^100
从而 lga1+lga2+...+lga100=lga1*a2*.*a99*a100
=lga1*a100*a2*a99*a3*a98*.*a50*a51
=lg10^100
=100
由{an}等比数列,得
a1*a100=a2*a99=a3*a98=.=a50*a51=100
而a1*a2*.*a99*a100=a1*a100*a2*a99*a3*a98*.*a50*a51=100^(100/2)=100^50=10^100
从而 lga1+lga2+...+lga100=lga1*a2*.*a99*a100
=lga1*a100*a2*a99*a3*a98*.*a50*a51
=lg10^100
=100
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