Hi, I'm sure this is a question with a simple answer. The code snippet explains it all. Maxima 5.9.0 GCL 2.5.3 thanks for any advice ... Judah /* This seems to work just fine: */ interpolate(x*sin(x)-1,x,0,%PI/2); /* but not this ? ... */ x*sin(x)-1$ interpolate(%,x,0,%PI/2);