Question

问几道关于log的题目1.已知log32(3小写）=a,2的b次方=3,求lga+lgb的值.2.已知a>1,b>1且a

Answer 1

1 lga+lgb=lg(ab)=lg(lg2/lg3*lg3/lg2)=lg1=0

2 2ab=2*8=16 lga x lg2b=lga*lg(16/a)=4lg2 max:lga=lg(16/a) a=4

3 log2x+log2（X-8）=log2(x-8)x=7 (x-8)x=2^7=128 x=16 x= -8(舍)

4 2^a=5^b=10 a=1/lg2 b=1/lg5 1/a+1/b=lg2+lg5=1