y=2^x .x^2y^(n) =(2^x)^(n) .x^2 + n(2^x)^(n-1) .(x^2)' + [n(n-1)/2] .(2^x)^(n-2) .(x^2)''=(ln2)^n . 2^x .x^2 +n(ln2)^(n-1) .2^x .(2x) +[n(n-1)/2] .(ln2)^(n-2).2^x .(2)y^(n)(0)=0 +0 +[n(n-1)/2] .(ln2)^(n-2).(1) .(2)=n(n-1).(ln2)^(n-2)