Re: Integration variables

*To*: mathgroup at smc.vnet.net*Subject*: [mg78351] Re: Integration variables*From*: dh <dh at metrohm.ch>*Date*: Thu, 28 Jun 2007 06:37:11 -0400 (EDT)*References*: <f5vr6e$j12$1@smc.vnet.net>

Hi mattew, obviously Cos[Theta] is not a variable but a function. If you want to use it as a varible you must give it a valid name,e.g. costheta. But then you must write the integrand as a function of your variable, e.g.: Integrate[ArcCos[costheta],{costheta,-1,1}] hope this helps, Daniel mattew wrote: > Hi everybody, Mathematica gives us the possibility to use spherical coordinates (r,Ttheta,Pphi): I'm trying to write an integral in the polar angle Ttheta of the form: > > Integral in [-1,1] Ttheta dCos(Ttheta) > > where Ttheta is the polar angle and the integration variable is the cosine of Ttheta in the interval [-1,1]. > > I got the following error: > > ntegrate::ivar: "Cos[Ttheta] is not a valid variable." > > Does anyone knows the reason for that? > > p.s: It happens with any system of coordinates, actually. >