RotateTransform of a line

I have a line and i want to rotate it about the center of the circle. But i want to get the coordinates of  the line which are being moved(the corrdinates of the end of the line which are NOT in the circle).

Here is my code plz help me:

my code in C#:

 double x = 0, y =0;

 private void Window_KeyDown_1(object sender, KeyEventArgs e)
        {
            if (e.Key == Key.Right)
            {
                RotateTransform trans = new RotateTransform(++y);
                trans.CenterX = 258;
                trans.CenterY = 285;
                linee.RenderTransform = trans;

            }
            else if (e.Key == Key.Left)
            {
                    RotateTransform trans2 = new RotateTransform(--y);

                    trans2.CenterX = 258;
                    trans2.CenterY = 285;
                    linee.RenderTransform = trans2;
                   
            }
            else if (e.Key == Key.Enter)
            {
                linee.Visibility = Visibility.Hidden;
                Canvas.SetLeft(ellipse, linee.X2 + 50);
                Canvas.SetTop(ellipse, linee.Y2 + 50);  
            }
            txt.Text = linee.X2.ToString()+ " " +linee.Y2.ToString() +" "+x.ToString();
        }

Code in XAML:

<Canvas Name="mycanvas">
        <Ellipse Height="50" Width="50" Name="ellipse" Stroke="Blue" Canvas.Left="233" Canvas.Top="260" >
            
        </Ellipse>
        <TextBox Name="txt" Height="50" Width="200">
            
        </TextBox>
        
        <Line Name="linee" Fill="#FFDA2828" Stroke="Black"
              X1="258" Y1="285" X2="258" Y2="70" 
              Visibility ="Visible"  StrokeThickness="2"
              StrokeDashArray="2,2,2 , 2">
            
        </Line>
    </Canvas>