Thank you for writing us back.
I'm assuming that you want to use our RadExpanderControl. It is included in our assembly Telerik.Windows.Controls.Primitives which also references our assembly Telerik.Windows.Core. In order to use the control, you need to add both references to your project. Then you need to declare a prefix, if you want to use the control in xaml. For example:
And then start using the control as any other control in WindowsPhone:
I have attached a demo application to illustrate the most simple usage of the control. If you want to see some more examples and information about this control, you can have a look at our online documentation here
If you still experience difficulties using this control you can send us your project, so that we can see what causes the issues.
the Telerik team
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