Android : change position of image view

i can't change the position of the login button.Because when i try, it can't be moved from the original position. I' ve set the android:layout_gravity and android:gravity but i want it in a specific position.

how i can set the coordinates (x,y) of the image?

this is the login_fragment.xml

LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_gravity="center"
    android:gravity="center"
    android:orientation="vertical" 
<ImageView
    android:id="@+id/login"
    android:layout_width="400px"
    android:layout_height="100px"
    android:src="@drawable/login_button" />