1.2log以5为底10+log以5为底0.25
=2log以5为底10+2log以5为底0.5
=2log以5为底10×0.5
=2log以5为底5
=2
2.已知lg2=0.3010,lg3=0.4771,
lg根号下45
=lg3+1/2lg5
=lg3+1/2(1-lg2)
=0.4771+1/2×(1-0.3010)
=0.4771+0.3345
=0.8116
3.【（1-log以6为底3）²+log以6为底2*log以6为底18】*log以4为底6
=【log²以6为底2+log以6为底2*(2-log以6为底2)】*log以4为底6
=【log²以6为底2+log以6为底2+log²以6为底2】*log以4为底6
=log以6为底2*log以4为底6
=lg2/lg6*lg6/lg4
=lg2/lg6*lg6/(2lg2)
=1/2