I add one part into my assembly. Then I decided to delete it because I cannot mirror or linear pattern the part. But I cannot delete it. In the feature tree there is a arrow front of the part symbol. Why I cannot delete the part from my assembly?
it is locked ,
you need to break the link first before you able to delete
Unlock the part, right click on part name and then hit delete or delete button. You can also make it float or locked if you want to change the mate.