private async void Calcular_Clicked(object sender, EventArgs e)
        {
            try
            {
                double x1 = Convert.ToDouble(txtX1.Text);
                double x2 = Convert.ToDouble(txtX2.Text);
                double r1 = Convert.ToDouble(txtR1.Text);
                double y1 = Convert.ToDouble(txtY1.Text);
                double y2 = Convert.ToDouble(txtY2.Text);
                double r2 = Convert.ToDouble(txtR2.Text);
                await Navigation.PushModalAsync(new Resulltado(x1, x2, y1, y2, r1, r2));

            }
            catch (FormatException)
            {
                await DisplayAlert("Error", "Debe ingresar todos los valores requeridos", "OK");

            }
            catch (Exception ex) {
                await DisplayAlert("Error", ex.Message, "OK");
            }

        }