Question on Gaussian Integral

1. Apr 11, 2013

liyz06

1. The problem statement, all variables and given/known data
I'm reading Hinch's perturbation theory book, and there's a statement in the derivation:
...$\int_z^{\infty}\dfrac{d e^{-t^2}}{t^9}<\dfrac{1}{z^9}\int_z^{\infty}d e^{-t^2}$...

Why is that true?

2. Relevant equations

3. The attempt at a solution
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Apr 11, 2013

Dick

Because 1/t^9 for t in (z,infinity) is less than 1/z^9. Draw a graph.

3. Apr 11, 2013

liyz06

Thanks, really stupid question