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绘制曲线的图象时,应用描点法固然能够确定某种曲线的走向,使我们认识该曲线的主要性质,但是,用描点法画的曲线有时不够全面,很难判断到底画得对不对。例如,要画y=x~3+2x+1的图象,可以确定一些点,取x=0、1、2、……6,便有相应的一些y值,为y=1、4、13、……229,见表1。见图1,图中X与Y轴所取的分度间隔不同,即两轴所用的比例不一样,绘制曲线时常这样做。图1所表示的图象有一个特点:x值增大1,y值增大约100(x=5至x=6);当x值为7、8、……时,每增大1,y值增大趋势更加明显地加剧。因此,不可能定出更
When drawing a curve image, applying the stroke method can certainly determine the direction of a certain curve, so that we can understand the main characteristics of the curve. However, the curve drawn by the stroke point method is sometimes not comprehensive enough, and it is difficult to judge whether the curve is correct. For example, to draw an image with y=x~3+2x+1, we can determine some points. Take x=0, 1, 2, ...6, then there will be some corresponding y values, which are y=1, 4, 13, ...... 229, see Table 1. See Figure 1. In the figure, the dividing intervals for the X and Y axes are different. That is, the ratios used for the two axes are different. This is often done when plotting curves. The image shown in Fig. 1 has one characteristic: the value of x is increased by 1 and the value of y is increased by about 100 (x = 5 to x = 6); when x is 7, 8, ..., every 1, y is increased. The trend of increasing values has been even more pronounced. Therefore, it is impossible to determine more