首先要知道公式：lg(a*b) = lga + lgb,lg(a / b) = lga - lgb;然后再看看这道题,lg根号15 = 0.5lg15 = 0.5lg(3 * 5) = 0.5(lg3 + lg5) = 0.5(lg3 + lg(10 / 2)) = 0.5(lg10 - lg2 + lg3) = (1 - a + b)/2;动动脑好好...