lg(2^x)+lg(8^y)
=lg(2^x)+lg(2^3y)
=lg(2^x*2^3y)
=lg[2^(x+3y)]=lg2
2^(x+3y)=2
x+3y=1
1/x+1/3y
=(1/x+1/3y)(x+3y) （因为后者等于1)
=2+3y/x+x/3y
3y/x+x/3y>=2根号(3y/x*x/3y)=2
所以1/x+1/3y>=2+2=4
最小值=4