绘制抛物线（带比例缩放）

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;

namespace WindowsApplication1
{
    public partial class Form1 : Form
    {
        private double a, b, c, d;
        private Graphics paper;
        private Pen pen = new Pen(Color.Black);

        public Form1()
        {
            InitializeComponent();
        }

        private void trackBarA_Scroll(object sender, EventArgs e)
        {
            DrawGraph();
        }

        private void trackBarB_Scroll(object sender, EventArgs e)
        {
            DrawGraph();
        }

        private void trackBarC_Scroll(object sender, EventArgs e)
        {
            DrawGraph();
        }

        private void trackBarD_Scroll(object sender, EventArgs e)
        {
            DrawGraph();
        }

        private void DrawGraph()
        {
            paper = pictureBox1.CreateGraphics();
            a = trackBarA.Value;
            labelA.Text = "a=" + Convert.ToString(a);
            b = trackBarB.Value;
            labelB.Text = "b=" + Convert.ToString(b);
            c = trackBarC.Value;
            labelC.Text = "c=" + Convert.ToString(c);
            d = trackBarD.Value;
            labelD.Text = "d=" + Convert.ToString(d);
            paper.Clear(Color.White);
            Draw();
        }

        private void Draw()
        {
            double x, y, nextX, nextY;
            int xPixel, yPixel, nextXPixel, nextYPixel;
            for (xPixel = 0; xPixel <= pictureBox1.Width; xPixel++)
            {
                x = ScaleX(xPixel);
                y = TheFunction(x);
                yPixel = ScaleY(y);
                nextXPixel = xPixel + 1;
                nextX = ScaleX(nextXPixel);
                nextY = TheFunction(nextX);
                nextYPixel = ScaleY(nextY);
                paper.DrawLine(pen, xPixel, yPixel, nextXPixel, nextYPixel);           
            }
        }

        private double TheFunction(double x)
        {
            return a * x * x * x + b * x * x + c * x + d;
        }

        private double ScaleX(int xPixel)
        {
            double xStart = -5, xEnd = 5;
            double xScale = pictureBox1.Width / (xEnd - xStart);
            return (xPixel - (pictureBox1.Width / 2)) / xScale;
        }

        private int ScaleY(double y)
        {
            double yStart = -5, yEnd = 5;
            int pixelCoord;
            double yScale = pictureBox1.Height / (yEnd - yStart);
            pixelCoord = (int)(-y * yScale) + (int)(pictureBox1.Height / 2);
            return pixelCoord;
        }
    }
}