已知log23=a,log35=b,求log1520
问题描述:
已知log23=a,log35=b,求log1520
答
lg3=alg2
lg5=blg3
lg20 = x lg15
2lg2+lg5 = x(lg3+lg5)
2lg2+blg3 = x(lg3+blg3)
2lg2+ablg2 = x(alg2+ablg2)
2+ab=x(a+ab)
x = (2+ab)/[a(1+b)]