有人懂c#的chart控件吗？我画了两条线，为什么会多出来一条线？
代码如图。大佬救急谢谢！
这是源码
namespace WindowsFormsApp1
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}

void drawline(double x1,double y1, double x2, double y2)//在两点间画线段
{
double k;
double b;
k = (y2 - y1) / (x2 - x1);
b = y1 - k * x1;
for (double x = Math.Min(x1, x2); x < Math.Max(x1, x2); x += 0.01)
{
double y = k * x + b;
chart1.Series["1"].Points.AddXY(x, y);
}
}

private void button1_Click(object sender, EventArgs e)
{
chart1.Series.Add("1");
chart1.Series["1"].ChartType = System.Windows.Forms.DataVisualization.Charting.SeriesChartType.Spline;
drawline(1, 1, 3, 3);
drawline(2, 4, 1, 3.5);
drawline(3, 3, 2, 4);
}
}
}