lg1∕2-lg1∕8+lg12.5-log8为底9乘以log3为底4=【 lg1∕2-lg1∕8+lg12.5】-log8为底9乘以log3为底4=lg(1/2÷1/8×12.5）-lg9/lg8×lg4/lg3=lg50-lg3²/lg2³×lg2²/lg3=lg50-3lg3/(2lg2)×2lg2/lg3=lg5...