lim(x→0) [(1+3^x+9^x)/3]^(1/x)
=e^lim(x→0) ln[(1+3^x+9^x)/3]^(1/x)
=e^lim(x→0) ln[(1+3^x+9^x)/3]/x
=e^lim(x→0) (3^x*ln3+9^x*ln9)/(1+3^x+9^x)
=e^ln3
=3