log的問題(please)

1. (8 ^x+1 )( 5^x)=120
(8 ^x+1)(5^x)=120
(8)(8^x)(5^x)=120
xlog8 + xlog5=log15
3xlog2 + x(1-log2)=log15
3xlog2 + x -xlog2=log15
2xlog2 + x =log15
x(2log2 + 1)= log 15
x = log15 / (2log2 +1)
x= log 15 / (log4 + log 10)
x= log15 / log 40
2.log3=a log5=b
1/2 log50
= 1/2 log(5x5x2)
=1/2log5 + 1/2log5 +1/2(1-log5)
=b/2 + b/2 + 1/2 -b/2
=b/2 + 1/2
=(1/2)(b+1)