设a=1/log4 (4为底)3+ 1/log7(7为底)3,则a的取值范围

设a=1/log4 (4为底)3+ 1/log7(7为底)3,则a的取值范围
设a=1/log4 (4为底)3+ 1/log7(7为底)3,则a的取值范围

设a=1/log4 (4为底)3+ 1/log7(7为底)3,则a的取值范围
a=1/log4 3+1/log7 3=log3 4+log3 7=log3 (4*7)=log3 28>log3 27=log3 3^3=3;得a>3;注意对数公式的灵活运用:1/loga b=1/(lgb/lga)=lga/lgb=logb a