How to deal with this integral

*To*: mathgroup at smc.vnet.net*Subject*: [mg97783] How to deal with this integral*From*: paperkite rainyday <paperkite at gmail.com>*Date*: Sat, 21 Mar 2009 05:19:41 -0500 (EST)

hi everybody, I want to deal with this integral with Mathematica: Integrate[a*b*Exp[-(a+b)]*DiracDelta[1/(4*a)+1/(4*b)+c-t],{a,0,Infinity},{b,0,Infinity},{c,0,Infinity},Assumptions->t>0], Mathematica 6.0 gives 0. But it is wrong, the correct result is (1/2)*x^2*Exp[-x]*((1+x)*BesselK[0,x]+(2+x+2/x)*BesselK[1,x]), where x=1/(2*t). What's wrong? Thanks, paperkite