a(n+1)=2an+3*2^n 两边同时除以2^(n+1)a(n+1)/2^(n+1)=an/2^n+3/2数列{an/2^n}是以a1/2=1/2为首项，3/2为公差的等差数列an/2^n=1/2+(n-1)3/2=(3n-2)/2an=(3n-2)/2*2^n
