Hide Mdi Parent form

Question

 I can hide mdi parent form by using
this.hide();

but i want to hide this mdi form from another form

ex:
  mdifrm1 ee=new mdifrm1 ();
  ee.hide();
 

this code is not working...
 

 I accepted and implement the answer ,
it is working but one time hide next time error because value of object 'mdi' is null,so null cannot hide

the implemented code is

mdiJewelSoft mdi = (mdiJewelSoft)this.MdiParent;

mdi.Hide();

how can repeatedly hide mdi?

 I think after hide ,how it show,?