搜搜做题作业网等比数列an中,有a3*a11=4a7,数列bn是等差数列,且b7=a7,则b5+b9=
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等比数列an中,有a3*a11=4a7,数列bn是等差数列,且b7=a7,则b5+b9=
a3·a11=4a7
a1q^2*a1q^10=4a1q^6
a1^2q^12=4a1q^6
a1q^6=4=a7=b7
b5+b9
=b1+4+b1+8d
=2b1+12d
=2(b1+6d)
=2b7
=2*4
=8
a1q^2*a1q^10=4a1q^6
a1^2q^12=4a1q^6
a1q^6=4=a7=b7
b5+b9
=b1+4+b1+8d
=2b1+12d
=2(b1+6d)
=2b7
=2*4
=8
等比数列an中,有a3*a11=4a7,数列bn是等差数列,且b7=a7,则b5+b9=
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