(1)y=loga(x+3)-1(a>0且a≠1),当x=-2时,loga(x+3)恒等于0,
∴y=loga(x+3)-1过定点A(-2,-1).
(2)A(-2,-1)在直线mx+ny+1=0上,则有-2m-n+1=0,即2m+n=1
1/m+2/n=(1/m+2/n)*(2m+n)=2+n/m+4m/n+2=4+n/m+4m/n>=4+2√[（n/m)*(4m/n)]=8
取等号的条件：n/m=4m/n,2m+n=1,得到m=1/4,n=1/2
∴(1/m+2/n)min=8,此时m=1/4,n=1/2