Rotates this vector through the given anti-clockwise angle
        in radians.

def get_rotated(self, angle):
        """Rotates this vector through the given anti-clockwise angle
        in radians."""
        ca = math.cos(angle)
        sa = math.sin(angle)
        return Point(self.x*ca-self.y*sa, self.x*sa+self.y*ca)