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a2a4+2a3a5+a4a6
=a1^2q^4+2a1^2q^6+a1^2q^8
=a1^2q^4(1+2q^2+q^4)
=a1^2q^4(q^2+1)^2
=[a1q^2(q^2+1)]^2
=25
an>0,a1>0 q>0
a1q^2(q^2+1)=5
a3+a5
=a1q^2+a1q^4
=a1q^2(1+q^2)
=5
在等比数列an中,若an>0且a2a4+2a3a5+a4a6=25,则a3+a5=(5).
1年前
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