I want to create a symmetric feature and after that delete the first (parent) feature. When I use the "mirror feature" after deleting of the first feature I lose the second feature too. What should I do to create that kinds of features?
Not seeing what it is that you are exactly making you can try several approaches:
1) copy the body using the "move/copy". Then use "delete body" on the first feature. "Delete Body" is a feature rather than just using delete.
2) let's say you're doing a cut extrude to get the first feature. Try the opposite. Create it as an extrude but do not merge results. This will give you a body that can be mirrored and then use the "subtract" command in the combine feature.
In other words it's a work around. the parent child relationship cannot be deleted directly once mirrored.
thank you so much Arthur...