# Calculators Trouble with multivariable limits of integration on Ti89

1. Sep 24, 2011

### aufbau86

Hello,

I'm currently trying to get my Ti-89 Titanium to compute the following triple integral;

f(x,y,z) = xy(1-z) where 0<x<1, 0<y<1, 0<z<1, and x+y+z<1

int(int(int(f(x,y,z),x,0,1-y-z),y,0,1-z),x,0,1)

The problem is that I can't get my Ti89 to substitute in for the limits of integration properly. For example, here is the result I get back after computing only the inner integral;

int(f(x,y,z),x,0,1-y-z) = -xy(1-z)(y+z-1)

It seems that it's holding the entire function constant whenever it has to interpret an integral at a limit which includes other variables. Basically it does this;

int(C,x,0,1-y-z) = C*int(1,x,0,1-y-z)
where C = Constant = f(x,y,z)

I've been trying to get it to work for a couple of infuriating hours, so I'm hoping one of you wizards can let me know how to get it to properly interpret integrals with multivariable limits of integration.

Thanks!

2. Sep 24, 2011

### ArcanaNoir

I don't have a TI-89, but try this http://www.mathcs.citadel.edu/~chenm/231.dir/07sp.dir/lect13_calculator_1.pdf [Broken]

Last edited by a moderator: May 5, 2017