如果括号里的是真数,
则log(30)90
=[log(30)2]/[log(90)2]
=[log(2)2+log(3)2+log(5)2]/[log(2)2+2log(3)2+log(5)2]
=(1+a+b)/(1+2a+b).
如果括号里的是底数,
则log(30)90
=[log(2)90]/[log(2)30]
=[log(2)2+2log(2)3+log(2)5]/[log(2)2+log(2)3+log(2)5]
=(1+2/a+1/b)/(1+1/a+1/b)
=(ab+a+2b)/(ab+a+b).