@Robert Israel I do apolagize if I have bothered you, I didn't mean it.
yes, something like this will help. Function definition is also correct but it fails at zero points of r and z, because in the integrand there is (for example) r*cos(teta) , by subsituting r=0 this one will be eliminated from integration which sounds wrong.
I have now 3 other questions. I will be glad if you (or any other person) could help me...
1. Is it possible for Maple to compute an integral false?
2. How can we reduce the computation time for an integral?(Still I have not examined your latest command line) Does Maple run slower than Mathlab for a similar program?
3. while running my program an error report appeared: "kernel connection has been lost" and it stopped running, needed to be restarted. How can I avoid this error?