How do I have to apply freeTransform around Its center to a vector shape

I do something wrong

<pre lang="c#">public void RotateTo(PointF p)
{
if (selection != null)
{

PointF c = new PointF(Selection.Rectangle.X + Selection.Rectangle.Width / 2, Selection.Rectangle.Y + Selection.Rectangle.Height / 2);


double x =c.X;
double y = c.Y;

double tempX = x * Math.Cos(90) - y * Math.Sin(90);
double tempY = y * Math.Sin(90)+ x * Math.Cos(90);
x =(float) tempX;
y =(float) tempY;
selection.Location = new PointF(c.X+(float)x-lastLocation.X, c.Y+(float)y-lastLocation.Y);
lastLocation = selection.Location;
}
}</pre>