<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <ImageButton
        android:layout_width="match_parent"
        android:layout_height="80dp"
        android:src="@drawable/sqrt"
        android:scaleType="fitCenter" />

</LinearLayout>