正文 第十八章 略懂略懂(第1页/共3页)
三角函数线解不等式通过三个解法。
正弦线，
余弦线，
正切线，
主要核心为具有三角函数值的有向线段方向和三角函数值的正负长度，以及绝对值。
仔细阅读完关于三角函数线解不等式的定义和内容，余华握着铅笔，在草稿纸上画了一个由Y轴和X轴构成的标准直角坐标系，中心点记0，接着又在半径为1的距离画了一个圆，自中心点0向第一象限作一条延长线，过圆。
延长线与中心点的角记α，延长线与圆的交点设A，过点A作X轴垂线，垂点记为B。
“所以，正弦线为有向线段→BA，余弦线有向线段→OB，正切线有向线段→CD，第二象限应该是这么画……”余华看的津津有味，昨晚学习到极限难以理解的三角函数线知识点简单而轻松，感觉全身再次充满力量，铅笔在草稿纸上重新画了一个直角坐标系和圆，根据知识点画出第二象限、第三象限和第四象限的三角函数线。
画了是四个不同的三角函数线象限，接下来是一道关于三角函数线解不等式的试题，源自剑桥大学数学教授哈代。
使sin x≤cos x成立之X之一个变化区间为多少。
“根据三角函数线，sinx=BA，cosx=0B，为了使sinx≤cosx成立，则变化区间应该为-3π/4≤x≤π/4，还是很简单的嘛，只要记好公式，直接套上去就完事了。”余华飞速计算，草稿纸迅速画出直角坐标系和圆构成，以中心点0向第一象限拉出一条延长线过圆，各自标记角和交点，三下五除二就解开试题。
这道题只要找出对应的三角函数线即可，只要找到线，那就好办，只需要计算X的数值范围即可，这点可难不倒身为小小学渣的余华。
简单，轻松。
再往下看，余华乐了，一大波试题，数量远比解析几何还多，更多关于三角函数线解不等式的基础试题和变化试题，基本都由剑桥大学的哈代教授所出，难度层层上升，目的就是为了提升学生的熟练度，增加经验。
当然，在无数学生们看来，哈代教授的良苦用心，完全变成了精心折磨。
“开冲开冲……”余华有些兴奋地搓了搓手，心中充满战意，吐出一口白色雾气，别人对于这波经验畏之如虎，他甘之如饴。
现如今，余华基本掌握高中算学80%左右的基础知识点，剩下的20%全是疑难重点，需要耗费大量时间和精力进行攻克，三角函数线就是其中之一。
试题越多，经验越丰富，小小学渣考取国立清华的目标，就会越来越近。
&nb
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