- #1
georg gill
- 153
- 6
Homework Statement
Integrate:
[tex]\int_{-\infty}^{\infty}\int_{-\infty}^{\infty}\int_{-\infty}^{\infty}e^{-2\sqrt{x^2+y^2+z^2}}dxdydz[/tex]
hint: use spherical integration
Homework Equations
[tex]p=\sqrt{x^2+y^2+z^2}[/tex]
[tex]dV=dp d\phi p sin\phi p d\theta[/tex]
The Attempt at a Solution
[tex]\int_{0}^{\infty}\int_{0}^{\pi}\int_{0}^{2\pi}e^{-2p} p^2 sin\phi d\theta d\phi dp[/tex]
look at integration for p since it is the most hard one first:
Integration by parts:
[tex]sin\phi\int_{0}^{\infty}e^{-2p} p^2 dp[/tex]
[tex]\int_{0}^{\infty}e^{-2p} p^2 dp=[\frac{e^{-2p}}{-2} p^2+\int_{0}^{\infty}e^{-2p}pdp]^{\infty}_0[/tex] (I)
[tex]\int_{0}^{\infty}e^{-2p}pdp=[\frac{e^{-2p}}{-2}p+\int_{0}^{\infty}e^{-2p}dp]^{\infty}_0=[\frac{e^{-2p}}{-2}p+\frac{e^{-2p}}{-2}]^{\infty}_0[/tex]
and (I) becomes:
[tex][\frac{e^{-2p}}{-2} p^2+\frac{e^{-2p}}{-2}p+\frac{e^{-2p}}{-2}]^{\infty}_0[/tex]
but here i get infinity in numerator and denumerator for [tex]p=\infty[/tex]. How do I solve this?