simplification of sin(0) and cos(0)



Dear List,

Please tell me if this is not the right place to ask this but I've run 
into a problem using maxima.

I have an expression (code below) involving a number of trigonometric 
functions. Now, I want to simplify this expression assuming certain 
variables are zero. This is, I want to assume that EL_1 and AZ_1 are 
zero. This would imply that my expression can be simplified as sin(0)=0 
and cos(0)=1. However, calling various simplification functions on sigma 
will not result in this (trivial) simplification.

What am I missing? Typing sin(EL_1); will result in 0.

Best, Dieter

sigma: sin(EL_1) * sin(EL_2) + cos(EL_1) * cos(EL_2) * cos(abs(AZ_1-AZ_2));
EL_1:0;AZ_1:0