log以2为底数,3为对数等于a,3的b次方等于7,求log以12为底数,56为对数

log2(3)=a则有：log3(2)=1/a由于：3^b=7则：log3(7)=b则：log12(56)利用换底公式：log12(56)=log3(56)/log3(12)=[log3(7)+log3(8)]/[log3(3)+log3(4)]=[b+log3(2^3)]/[1+log3(2^2)]=[b+3log3(2)]/[1+2log3(2)]=[b+3/a]/[1+2/a]=[ab+3]/[a+2]