Question

高中数学数列问题

高中数学数列问题求此题答案划住的地方其详细过程

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Answer 1

an=a1.q^(n-1)
a3.a8=81
(a1)^2.q^9=81 (1)
log<3>a1+log<3>a2 +...+log<3>a10
=log<3> (a1.a2....a10)
=log<3>[ (a1)^10. q^45]
=5log<3>[ (a1)^2. q^9]
=5log<3>81
=5(4)
=20

追问

q的45次方如何求得

追答

log (a1.a2....a10)
=log[ a1^10 . q^(0+1+2+...+9) ]
=log[ (a1)^10. q^45]
=log[ (a1)^2. q^9]^5
=5log[ (a1)^2. q^9]
=5log81
=5(4)
=20