If [tex]f(x)=x^2e^{-x^3}[/tex], then the area between the graph of [tex]f(x)[/tex] and the x-axis for non-negative x is given by the integral,
[tex]\displaystyle\int_0^\infty x^2e^{-x^3}\,\mathrm dx[/tex]
Let [tex]u=-x^3[/tex] and [tex]\mathrm du=-3x^2\,\mathrm dx[/tex]; then the integral is equivalent to
[tex]\displaystyle-\frac13\int_0^{-\infty}e^u\,\mathrm du=\frac13\int_{-\infty}^0e^u\,\mathrm du=\frac13\left(1-\lim_{u\to-\infty}e^u\right)=\boxed{\frac13}[/tex]
