用五点法作函数的图像
例1、用五点法作下列函数的图像
（1）![](https://wkrtcs.bdimg.com/rtcs/image?w=151&md5sum=64bd6e218243015aa343612d12dba192&sign=88158ebe6d&rtcs_flag=1&rtcs_ver=3&l=webapp&bucketNum=98&ipr={"t":"img","w":"151","h":"20.466666666667","dataType":"gif","c":"word/media/image1.png"})
（2）![](https://wkrtcs.bdimg.com/rtcs/image?w=196.33333333333&md5sum=64bd6e218243015aa343612d12dba192&sign=88158ebe6d&rtcs_flag=1&rtcs_ver=3&l=webapp&bucketNum=98&ipr={"t":"img","w":"196.33333333333","h":"41","dataType":"gif","c":"word/media/image2.png"})
分析：利用五点法作图关键找出这五个点：最高点、最低点、与x轴的交点，根据正弦曲线的图象特点画出大致图象．
解：（1）
| 0 |
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| 0 | 1 | 0 | －1 | 0 |
| 2 | 1 | 2 | 3 | 2 |
描点作图（图（1））
（2）
| 0 |
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| 1 | 0 | －1 | 0 | 1 |
描点作图（图（2））
![](https://wkrtcs.bdimg.com/rtcs/image?w=472.46666666667&md5sum=64bd6e218243015aa343612d12dba192&sign=88158ebe6d&rtcs_flag=1&rtcs_ver=3&l=webapp&bucketNum=98&ipr={"t":"img","w":"472.46666666667","h":"201.73333333333","dataType":"jpeg","c":"word/media/image17.png","imgOriW":718,"imgOriH":306})
小结：“五点法”作图，要抓住五个关键点，使函数中![](https://wkrtcs.bdimg.com/rtcs/image?w=48.533333333333&md5sum=64bd6e218243015aa343612d12dba192&sign=88158ebe6d&rtcs_flag=1&rtcs_ver=3&l=webapp&bucketNum=98&ipr={"t":"img","w":"48.533333333333","h":"20.466666666667","dataType":"gif","c":"word/media/image18.png"})
取，然后求出相应的x，y值．
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![](https://wkrtcs.bdimg.com/rtcs/image?w=17.266666666667&md5sum=64bd6e218243015aa343612d12dba192&sign=88158ebe6d&rtcs_flag=1&rtcs_ver=3&l=webapp&bucketNum=98&ipr={"t":"img","w":"17.266666666667","h":"41","dataType":"gif","c":"word/media/image4.png"})
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