Re: Add the Logarithms (error in integral)

*To*: mathgroup at smc.vnet.net*Subject*: [mg25106] Re: Add the Logarithms (error in integral)*From*: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>*Date*: Sun, 10 Sep 2000 03:14:29 -0400 (EDT)*Organization*: Universitaet Leipzig*References*: <8p9j71$1fl@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

Hi, h1 = h //. a_.*Log[b_] + c_.*Log[d_] :> Log[b^a*d^c]; Chop[N[h1 /. {a -> 10, b -> 10}]] 0.000716695 Regards Jens Jos R Bergervoet wrote: > > I'm trying to integrate a function f over a triangle with vertices: > (0,0), (a,0), (0,b). My input is: > > f = 1/ Sqrt[1+x^2+y^2]^3 > g = Integrate[f, {y,0, b-b x/a} ] > h = Integrate[g, {x,0,a}] > N[ h /. {a->10, b->10} ] > > With a=b=10, the output for this positive(!) function is negative: > > Out[4]= -4.91074 + 0. I > > which is obviously wrong. > > Looking at the answer with FullSimplify[h] I see it contains 4 > logarithms (see answer at the end of this message). Is there any > way to add these logarithms? (into one logarithm with the product > of the original arguments?) > > FullSimplify refuses to do this. Is there another way? > > Thanks in advance, > Jos