若log₃2=a,则log₃8-2log₃6用a表示为?1.a-2 2.5a-2.3.3a-(1+a)² 4.3a-a²-1

若log₃2=a,则log₃8-2log₃6用a表示为?1.a-2 2.5a-2.3.3a-(1+a)² 4.3a-a²-1
若log₃2=a,则log₃8-2log₃6用a表示为?1.a-2 2.5a-2.3.3a-(1+a)² 4.3a-a²-1

若log₃2=a,则log₃8-2log₃6用a表示为?1.a-2 2.5a-2.3.3a-(1+a)² 4.3a-a²-1
log₃8-2log₃6
=log₃2³-2log₃(2×3)
=3log₃2-2(log₃2+log₃3)
=3a-2(a+1)
=3a-2a-2
=a-2
所以是1

log3(8)=3log3(2)=3a
2log3(6)log3(36)=log3(4*9)=log3(4)+log3(9)=2log3(2)+2log3(3)=2a+2
∴log3(8)-2log3(6)=3a-2a-2 =a-2
选1