It looks like you want to find
[tex]\displaystyle \int t^{11} e^{-t^6}\,\mathrm dt[/tex]
Substitute u = -t ⁶ and du = -6t ⁵ dt. Then
[tex]\displaystyle \int t^{11} e^{-t^6}\,\mathrm dt = \frac16 \int (-6t^5) \times (-t^6) e^{-t^6}\,\mathrm dt = \frac16 \int ue^u \,\mathrm du[/tex]
Integrate by parts, taking
f = u ==> df = du
dg = eᵘ du ==> g = eᵘ
Then
[tex]\displaystyle \frac16 \int ue^u \,\mathrm du = \frac16\left(fg-\int g\,\mathrm df\right) \\\\ =\frac16 ue^u - \frac16\int e^u\,\mathrm du \\\\ =\frac16 ue^u - \frac16 e^u + C \\\\ =-\frac16 t^6 e^{-t^6} - \frac16 e^{-t^6} + C \\\\ =\boxed{-\frac16 e^{-t^6} \left(t^6+1\right) + C}[/tex]
