∵a=log(2)3=lg3/lg2,3^b=7 ∴b=lg7/lg3 ∴lg7=blg3=ablg2,lg3=alg2 ∴log(42)56=lg56/lg42 =(lg8+lg7)/(lg2+lg3+lg7) =(3lg2+ablg2)/(lg2+alg2+ablg2) =(ab+3)/(ab+a+1)