silverlight - How to create a rounded corner rectangle

how to create rounded corner rectangle in silverlight
MainPage.xaml

<UserControl 
    x:Class="SilverlightApps.MainPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d"
    d:DesignHeight="600" 
    d:DesignWidth="800" 
    xmlns:sdk="http://schemas.microsoft.com/winfx/2006/xaml/presentation/sdk"
    >

    <Grid x:Name="LayoutRoot" Background="White">
        <TextBlock 
            Height="82" 
            HorizontalAlignment="Left" 
            Margin="20,12,0,0" 
            Name="textBlock1" 
            Text="Silverlight - how to create rounded corner rectangle"
            VerticalAlignment="Top"
            TextWrapping="Wrap"
            FontSize="20"
            FontStyle="Italic"
            Foreground="MidnightBlue"
            Width="625"
            />

        <Rectangle 
            Name="rectangle1"
            Fill="SeaGreen" 
            HorizontalAlignment="Left" 
            Height="100" 
            Margin="36,75,0,0" 
            VerticalAlignment="Top" 
            Width="100" 
            RadiusX="3" 
            RadiusY="5" 
            StrokeThickness="2"
            >
        </Rectangle>

        <Rectangle 
            Name="rectangle2"
            Fill="DeepPink" 
            HorizontalAlignment="Left" 
            Height="100" 
            Margin="167,75,0,0" 
            VerticalAlignment="Top" 
            Width="172" 
            RadiusX="10" 
            RadiusY="10" 
            StrokeThickness="2"
            >
        </Rectangle>

        <Rectangle 
            Name="rectangle3"
            Fill="Orchid" 
            HorizontalAlignment="Left" 
            Height="100" 
            Margin="361,75,0,0" 
            VerticalAlignment="Top" 
            Width="131" 
            RadiusX="25" 
            RadiusY="15" 
            StrokeThickness="2"
            >
        </Rectangle>
    </Grid>
</UserControl>
MainPage.xaml.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Shapes;

namespace SilverlightApps
{
    public partial class MainPage : UserControl
    {
        public MainPage()
        {
            InitializeComponent();
        }
    }
}
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