@Carl Love 

thank you very much

@gkokovidis 

thank you so much

@gkokovidis 

thank you so much

@Markiyan Hirnyk 

Thank you so much

@Markiyan Hirnyk 

I will try what you said,

Thanks a lot,

@Markiyan Hirnyk 

I mean Probability Density Function of a continuous variable. For instance, x is a randon continuous variable with pdf f(x)

I want to calculate the integral of xf(x) dx.

I read the help, but what I read is all works in maple worksheet mode.

I am wondering how can I do it in document mode.

@Markiyan Hirnyk 

yes I mean pdf.