log(2)(1/49)*log(3)(1/16)*log(7)(1/27)=log(2)7^(-2)*log(3)2^(-4)*log(7)3^(-3)用换底公式=[lg7^(-2)/lg2]*[lg2^(-4)/lg3]*[lg3^(-3)/lg7]=(-2)*(-4)*(-3)*lg7*lg2*lg3/(lg2*lg3*lg7)=-24