若f(x)=3x+4,f1(x)=f(x),f2(x)=f(f1(x)),f3(x)=f(f2(x)),···,···,fn(x)=f(fn-1(x)),n属于N*,则f(f(···f(x)))=?注：共n个

若f(x)=3x+4,f1(x)=f(x),f2(x)=f(f1(x)),f3(x)=f(f2(x)),···,···,fn(x)=f(fn-1(x)),n属于N*,则f(f(···f(x)))=?注：共n个
若f(x)=3x+4,f1(x)=f(x),f2(x)=f(f1(x)),f3(x)=f(f2(x)),···,···,fn(x)=f(fn-1(x)),n属于N*,则
f(f(···f(x)))=?注：共n个

若f(x)=3x+4,f1(x)=f(x),f2(x)=f(f1(x)),f3(x)=f(f2(x)),···,···,fn(x)=f(fn-1(x)),n属于N*,则f(f(···f(x)))=?注：共n个
f1(x)=3x+4
f2(x)=3(3x+4）+4=3^2x+3·4+4
f3(x)=3（3^2x+3·4+4）+4=3^3x+3^2·4+3·4+4
·····
fn(x)=3^nx+3^（n-1)·4+3^(n-2)·4+···+3·4+4
=3^nx+4[1+3+3^2+3^3+····+3^（n-1)]
=3^nx+2·3^n-2